GEOLOGICAL SKETCHES 


OF THE 


PRECIOUS METAL DEPOSITS 

OF THE 

WESTERN UNITED STATES, 


BY 


vW ■ 

S. Ef EMMONS AND G. F. BECKER, 


*> 


WITH-NOTES ON 


LEAD SMELTING AT LEADVILLE. 



EXTRACT FROM THE TENTH CENSUS OF THE UNITED STATES, VOL. XIII “STATISTICS AND 

TECHNOLOGY OF THE PRECIOUS METALS.” 



> * 




WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 

1 8 85 . 






















































f 


v? V 

STATISTICS AND TECHNOLOGY OF THE PRECIOUS METALS. 


Chapter I.—GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 

By George F. Becker. 


It is the purpose of this chapter to present such au outline of the geology of each of the states and territories 
west of the Rocky mountains as will serve to assist those unfamiliar with the country in forming an idea of the 
character and distribution of its mineral resources, and to convey such rudimentary information concerning the 
relations which the ore deposits bear to the larger features of the geological structure as is necessary to an 
intelligent perusal of the statistical chapters. The information available for this purpose is far from ample. The 
government geological explorations of the last twenty years have done a large amount of extremely valuable work, 
some of which has made a permanent mark on the history of the science; but the territory is so vast that many 
decades must elapse before even the preliminary explorations are completed. The collections and the data gathered 
by the census experts are also very valuable. Few mines, however, can be properly understood without a somewhat 
extended examination of the surrounding country, for which the experts had no time, and the information is therefore 
rather fragmentary. 

The order adopted in sketching the states and territories is not that which would have been chosen had the 
information been more complete. Washington territory and Oregon are placed after California, because little is 
known of them directly, while certain inferences maybe legitimately drawn from the analogous territory embraced 
in the last-named state, and Idaho is described after Nevada and Utah for similar reasons. 

The regularity of the distribution of ores in the Pacific division and its relations to the singularly uniform 
topography long ago drew the attention of writers to the resources of this region. Mr. W. P. Blake (a) first 
published a note on the subject in 1866, and his statement was accepted and enlarged upon by Mr. King (b) in 
1870. The more detailed technical and scientific investigations of later years have greatly increased our knowledge 
of the distribution and extent of the ores, and it will now scarcely be maintained that there are more thaurfour well- 
defined and continuous ore belts west of the Rocky mountains. Beginning at the east, the first is that at the 
western foot of the Wahsatch and the southwestern continuation of that range. With the exception of the Leeds 
(Silver Reef) district, all the important ore deposits of Utah lie in the foot-hills of this range, bearing a very definite 
relation to the main line of crests. The gold and copper belt of California stands for a long distance in a similar 
relation to the Sierra Nevada. The quicksilver belt in the California coast ranges is not quite so regular in its 
occurrence, yet its direction is very nearly parallel to the coast, and it is very persistent, though nowhere broad, for 
some 300 or 400 miles. The Arizona belt is less known than any of the others, but no one can glance at a map of 
the territory showing the mining districts without perceiving that these lie in a northwestern and southeastern 
line diagoually across the country. The mining districts in Nevada are extremely numerous, so much so indeed 
that some grounds could be given for assuming a belt to run in almost any desired direction, but they are scarcely 
close or regular enough in any one line to compel the observer to regard them as connected. 

These four distinct belts appear to have an intimate connection with the four great orograpliieal changes which 
the region west of the Rocky mountains has undergone during its geological history. The last of these was post- 
Miocene, and resulted in the uplift of the Pacific Coast ranges and the great interior valley of California, with a large 
part of Oregon and Washington territory. The disturbing force seems to have been most powerful to the north and 
south of San Francisco, or approximately in the region marked by the quicksilver deposits. A post-Cretaceous- 
upheaval raised the whole western central portion of the continent now occupied by the complex system of the 


a Annotated catalogue of the principal mineral speciea hitherto recognized in California, etc. 

p. 26 . 

b Exploration of the 40th Parallel, iii, p. 6. 


Report to state hoard of agriculture,. 


r> 








6 


PRECIOUS METALS. 


Eocky mountains. The Wahsatch forms the western edge of this uplift, and the dislocation took place on an old 
fault coincident with the present western foot of that range. Here also lie the numerous mines of Utah. The 
Sierra Nevada and the ranges of the Great Basin were raised by a post-Jurassic uplift. The line of most intense 
disturbance coincided with the Sierra, and the greatest dislocation occurred along its western foot, in the gold belt, 
though it also extended to the south of that wonderful series of deposits. The earliest disturbance in the far west 
was that which raised the Palaeozoic strata of eastern Nevada, western Utah, and a portion of Arizona above the 
surface of the ancient sea. The western limit of this Palaeozoic area has been traced in detail across the belt 
surveyed by the exploration of the fortieth parallel, and in that latitude it trends nearly north and south in 
longitude 117°30'. "To the south the limit has been fixed at a considerable number of points, though it has not been 
followed in detail. South of Austin the course of the western edge of the Palaeozoic is somewhat west of south, and 
it enters California a little north of Owen’s lake. In this region it is deflected toward the southeast, crosses the 
Colorado river in Virgin canon, passes by Prescott, and on through Arizona to the neighborhood of Tombstone. 
The main Arizona belt of deposits has the same trend as the border of the Palaeozoic, and nearly coincides with it 
in position. In short, though the relation still requires much investigation, the Arizona mineral belt appears to 
stand in nearly the same relation to the western edge of the post-Carboniferous upheaval as do the belts of Utah 
and California to the other uplifts. That these relations exist as a matter of fact is beyond question, though it is 
possible that they may be accidental. In any case, however, the uplifts, as such, are not to be regarded as the cause 
of the formation of the mineral belts; these must rather be due to the Assuring of the rocks and the dislocations 
attending the orographical changes. There is evidence that the post-Carboniferous uplift in the state of Nevada 
and in southeastern California was comparatively gentle, and that it was not attended by any considerable crumpling 
of the strata. This would account for the fact that the number of ore deposits at its edge in these states is not 
very large. Nevertheless, the lead deposits of Battle Mountain, the Austin mines, the Candelaria district (which 
includes the famous Northern Belle mine), Panamint, and Cerro Gordo all occur at or close to the western edge of 
the Palaeozoic. Taken in connection with the geological similarity of their position to that of the Arizona mines, 
these deposits may perhaps fairly be regarded as the rudiments of a belt. In Arizona the area in which the contact 
occurs has been too little investigated to allow of any statement as to the violence of the uplift, but, all things 
considered, it would be remarkable if it should not ultimately prove to have been attended by much disturbance. 

This theory of a relation between the ore-belts and the lines of uplift is, of course, not to be understood as 
equivalent to the assertion that the deposits are to be found only along a single line representing the actual main 
fissure of the uplift. One is apt to think of the dislocation attending an orographical change as confined to a single 
vertical or highly inclined surface, but every geologist is aware that this is not an exact view. Simple fissures in 
the earth’s crust are very rare, and parallel sets of fissures, with cross fractures and stringers into the surrounding 
country, are the rule even in the case of insignificant cracks. In disturbances such as those of the great uplifts 
a considerable belt of country is almost necessarily crushed and torn, and innumerable rents and cracks standing 
in most complex relations to one another penetrate the rocks in many directions. The breadth of such a zone 
must usually be measured in miles. 

It may be that some of the ore deposits of the Pacific division are independent of volcanic action, but the 
association of eruptive rocks with ores is a rule with comparatively few apparent exceptions, and in many cases the 
agency of solfatarie action (a) is manifest. This has long been recognized by observers. 

That there are relations between the rocks inclosing ore deposits and the character of the ores has been known 
to miners for centuries, but the study of the nature of this dependence is comparatively new. It is far too complex 
a subject to be discussed in this chapter, but it may at least be stated that the census collections and data appear 
to confirm, emphatically, the existence of such relations. Lead ores are almost invariably accompanied by limestone, 
and veifis in granite present only a very small number of associations of minerals, which are possibly reducible to 
a single one. Deposits in metamorphic rocks, too, though more varied than the others, appear to represent but a 
few types. It was not practicable, however, for the experts to make such minute examinations of the mines as 
would have been necessary to furnish material for a conclusive investigation of this subject. 

With some hesitation most of the determinations of the ore and gangue minerals, the country rocks, and the kind 
of deposit, arc introduced county by county. There can be no doubt that the list of ore minerals is often imperfect. 
The determination of the wall rocks is subject to some uncertainty without a thorough examination in the field as 
well as in the study, and the nature of a deposit is in many cases not to be decided by a single visit. It is 
probable, however, that the determinations of rocks and minerals are nearly always correct as far as they go, and in 
the cases in which the character of the ore deposits was not clear as much may generally be inferred from the statement 
regarding them. The tables, therefore, contain much information of value, and many suggestions to such geologists 
and miners as are careful to remember that they are not exhaustive statements. Except in a few cases, in which 
I happened to have visited the localities, the determination of the character of the deposits rests on the authority 
of the experts. The determinations of rocks and minerals inclosed in parenthesis are also due to the experts, 


a As originally employed, the term solfatarie action denoted only the effect of gaseous emanations front volcanic vents. In use, 
however, it has gradually come to include the action of heated waters charged with these gases or holding them in solution, and ia so 
employed in this chapter. 



GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


7 


while the remainder I have made from the specimens collected by my assistants. The difficulties met with in 
making these determinations were considerable, for rocks near ore deposits are usually much altered, and the ore 
minerals need much closer attention than in ordinary specimens of merely mineralogical interest. A few minute 
particles of such minerals in a hand specimen often make the difference between waste rock and rich ore and the 
inspection of the samples needed to be correspondingly searching. 

Maps of the states and territories of the Pacific division accompany the sketches. These are necessarily on a 
small scale, but present the leading features sufficiently well to assist the reader in following the descriptions. On 
them are entered signs indicating the distribution of gold, silver, and quicksilver. These are not designed to 
represent every spot where precious metals have been detected, but to indicate at a glance their general distribution. 

GEOLOGICAL SKETCH OF CALIFORNIA. 

The mineral resources of California are extremely varied, but are also of very unequal importance. Its gold 
production is an essential factor in determining the relations of the mediums of exchange throughout the world, its 
total value since 1849 exceeding $1,200,000,000. Its quicksilver production, also, though of far less value, exceeds 
that of any other country. The total known product of California from 1850 to the close of 1880 was a trifle less 
than 91,000,000 pounds, of an average value of 71 cents, and has yielded above $65,000,000. It is important as an 
adjunct to the precious-metal industries no less than as an independent source of profit. The silver product yields 
above a million per year ; and the coal-fields, though not of the best, furnish a large part of the supply necessity 
for home consumption. Asphalt anti petroleum are obtained in small quantities, and some sulphur and borax are 
extracted, while lead is reduced only as an incident of the silver industries, and copper and iron, though their ores 
are plentiful, are worked on a small scale only. Tin, chromic iron, black oxide of manganese, and other useful 
minerals also occur in the state, but as yet contribute little to its commercial prosperity. 

The great industrial importance of the gold production of California has drawn the attention of many geologists 
and engineers to the geology of the state, and the literature on the subject is comparatively extensive. The Pacific 
railroad survey, Mr. J. A. Phillips’ work on gold and silver, the reports of the mining commissioners, the 
proceedings of the California Academy of Sciences, and the scientific journals of America and Europe, all contain 
contributions to the subject; but the chief source of authority is the volumes of the state geological survey of 
California, conducted under the charge of Professor J. D. Whitney, who had the assistance of Messrs. Clarence 
King, W. H. Brewer, W. M. Gabb, ‘William Asliburner, W. H. Pettee, and others. Unfortunately, the legislature 
ceased to appropriate funds for the survey iu 1874 before a single geological map had been issued. Professor 
Whitney, however, has continued to work up the material collected, and has issued a number of volumes during 
the last eight years. The census reports and collections also furnish some information of value from a geological 
point of view, but the following sketch owes most to the data collected by Professor Whitney and his assistants 
or recorded in the volumes published under his supervision. 

The interior of California forms a long, oval valley. Its greater diameter is parallel to the coast, and extends 
from the neighborhood of Fort Tejon to Mount Shasta, a distance of 450 miles, while the average width is about 
40 miles. This valley is surrounded by mountains, except at a single point, where San Francisco, San Pablo, and 
Suisun bays afford an outlet for the drainage gathered by the Sacramento river from the north and the San Joaquin 
from the south. 

Though the mountain ranges inclosing this basin unite at its extremities, the Great Valley is not a mere 
undisturbed area between different ranges of a complex chain; on the contrary, the Sierra Nevada to the east and 
the Coast ranges to the west represent upheavals of different characters and widely distant eras. The Sierra 
Nevada is a single range forming the western rampart of the elevated plateau of the Great Basin, and was raised 
in post-Jurassic times. The Coast ranges consist largely of detritus from the Sierra; they were uplifted for the 
most part at the end of the Miocene, and constitute a mountainous belt of country to which even the name of 
chain can scarcely be applied. No term answering to the Coast ranges was used by the Spanish settlers of the 
country, but they gave special names to a considerable number of small ranges within the Coast belt, and these are 
still in use. The elevation of the Coast ranges is greatly inferior to that of the Sierra, a number of peaks of the 
latter exceeding 14,000 feet, while none of the culminating points of the Coast ranges appear to rise more than 
6,000 feet above sea level. * 

Both the Sierra Nevada and the Coast ranges are greatly metamorphosed and contain extensive deposits of 
useful minerals, and the alteration of the strata and the deposition of ore are probably in each case related 
phenomena; but the metamorphosis and ore-deposition of the Coast ranges occurred long after the cessation of 
similar activity in the Sierra, and led to widely different results. The more remarkable deposits of the Coast 
ranges are cinnabar, chromic iron, coal, asphalt, and mineral oil, while gold and copper are characteristic of the 
western slope of the Sierra, lead and more or less auriferous silver occurring very extensively on the eastern slope, 
of which only a portion lies within the limits of the state. 

The backbone of the Sierra is granitic, the higher summits and a large part of the western slope of the 
range being of this rock, except in the northern portion of the state, where it has been covered by basaltic and 


8 


PRECIOUS METALS. 


andesitic lavas. The granite penetrates some of the accompanying strata in dikes, and Professor Whitney regaich 
it as beyond question of eruptive origin, while some other geologists see in it only highly metamorphosed sedimentary 
material reduced to a plastic state in situ. Except at the northern end of the Great Valley, near Mount Shasta, 
and near Owen’s lake, no Palaeozoic strata have been identified. In the Gray mountains, Shasta county, a limited 
area of Carboniferous limestone occurs, amply identified by fossils. A small amount of limestone with the same 
external characteristics occurs farther south, and Professor Whitney regards it as not improbably of the same age. 
From a mining poiut of view, however, it is insignificant, carrying little gold. The principal strata on the west flank 
of the Sierra are Jurassic and Triassic, occurring chiefly and characteristically as slates and shales. They are highly 
metamorphic, contain few fossils, and have been profoundly disturbed, showing that the range was uplifted since their 
deposition. These are the main gold-bearing rocks, and will be more particularly.described further on. Near the 
foot of the range are areas of Cretaceous and Tertiary beds, chiefly marine, nearly horizontal, and resting unconfqrm- 
ably on the upturned auriferous slates. Above the Mesozoic slates lie fresh water auriferous gravels, mainly of 
Tertiary age, and these toward the north are in part covered by flows of Tertiary and post-Tertiary lavas. Inyo and 
Mono counties lie to the east of the Sierra. The metamorphic slates and limestones of this region are for the most 
part Triassic, though the Jurassic is probably also represented, and are covered to a great extent by volcanic rocks. 
Mr. Gilbert has shown that the eastern edge of Inyo county reaches the Palaeozoic area. 

The Jura-Trias strata extend to the east of the Sierra about as far as longitude 117° 30'. They rest directly 
upon Archaean schists and granite, and the long interval of time which they represent seems to have been extremely 
q»iet, for no non-conformity has been detected in the series. At the close of the Jurassic, however, the whole 
area from the western foot of the Sierra to the middle of the state of Nevada was raised above the ocean and 
compressed from west to east, resulting in the formation of a number of parallel ranges, of which the most westerly 
were the Sierra Nevada and the Blue Mountain range of Oregon. Ore deposits occur on the eastei n as well as on the 
western flank of the Sierra, but their character and mode of occurrence differ from those prevailing in the gold belt. 

The Coast ranges, or the western mouutaiuous belt between Mount Shasta and fort Tejon, are for the most part 
composed of more or less altered rocks of Cretaceous and Tertiary age. The geologists aud the paleontologists of the 
state survey divided the Cretaceous into lower aud upper, and, while recognizing the later divisions of the Tertiary, 
failed to find anything certainly corresponding to Eocene. Of late, however, it has been shown that the fossils of what 
had been considered as the Upper Cretaceous exhibit strongly marked Tertiary affinities, aud it seems by no means 
impossible that the beds in question, which are sometimes called the T6jon group, and include the Monte Diablo 
coal-fields, really represent the Eocene. Considering that differences of climate must always have existed, whether 
more or less marked than those of the present time, it is not strange that doubtful cases like those of the T6jon 
group, the Laramie beds, and the Australian coal-bearing rocks occur, but rather that it is so often possible to 
determine the correspondence of strata in widely separated areas. 

Though the Coast ranges here aud there show granitic rocks, granite is of only local importance, and does not 
appear to form the central mass, as is the case with the Sierra. The body of these ranges is made up of crumpled 
and fractured strata, indicating, according to Professor Whitney, sharp and sudden elevations and depressions, 
extending through the Pliocene epoch. To the southward the prevailing rocks are Tertiary, but north of the bay 
of San Francisco these almost disappear, the Cretaceous becoming predominant. Volcanic rocks are not widely- 
spread, most of the known occurrences being found between San Fraucisco and Clear lake. 

It appears, therefore, that the elevation of the coast as a whole was comparatively recent. While the quartz 
veins were forming, aud while the gravels were accumulating on the west flank of the Sierra, the region of the 
Coast ranges and the Great Valley were wholly or partly under a gulf or sea, shallow in parts and surrounding 
more or less extensive islands. The existence of this shallow sea must have had an important influence oh the 
climate of the Sierra, for, supposing the evaporation to have been the same, nearly the whole amount of moisture 
now distributed through the Coast ranges and the interior of California would have fallen on the Sierra in addition 
to its present rainfall. But evaporation is considerably more rapid from shallow seas than from deep ones, and 
the rainfall on the Sierra must consequently" have been enormous. The chief uplift of the Coast ranges took place 
at the close of the Miocene, and the great metamorphism aud ore deposition are probably for the most part referable to 
the same period, though it is likely" that the still later volcanic eruptions induced a portion of them. The Pliocene 
or i>ost-Pliocene disturbances were comparatively gentle, but Professor Whitney regards the break at the Golden 
Gate, the prevalence of volcanic rocks from that point north to Clear lake, and the disturbances of the Pliocene 
south of San Francisco bay, as connected phenomena. 

The region south of fort T6jon has been much less investigated than the central portion cf the state. It 
appears to possess some extremely interesting geological features, but also to present unusual difficulties. The 
San Gabriel range north of Los Angeles has a granitic axis, and it is possible to trace this granite ridge 
uninterruptedly" through Los Angeles, San Bernardino, and San Diego counties into Lower California, and along 
the peninsula to within a few miles of the old mission of Santa Gertrudis. (a) The sedimentary- rocks accompanying 
this granite ridge are for the most part highly- metamorphosed, and are frequently penetrated by dikes of granite. 
They are nevertheless considered by both Professor Whitney and Mr. Gabb as of Cretaceous and Tertiary age, and 
the uplift is referred, like that of the Coast ranges proper, to the close of the Miooene. 


a Geological Survey of California, ii, 137. 




GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


9 


Besides the bitumen springs of Ventura and Los Angeles counties, there are gold mines in this southern 
California range, but few details have been published as to their occurrence, and their geological relations are still 
to be studied. 

The character of the rocks of the Coast range shows that the Cretaceous and Tertiary sea near the present 
coast was shallow, but there is evidence that the Great Valley represents a former depression of immense depth. 
This, however, would not prevent the gulf at the foot of the Tertiary Sierra from being as warm, for example, as 
the Gulf of Mexico, for the temperature of the water of a land-locked basin depends on the depth of the inlet to it, 
and if this is small the water of the basin will be warm. 

In Russia and Australia the Silurian is the gold-bearing formation, and Sir Roderick Murchison enunciated the 
somewhat rash generalization that gold was to be looked for only in the Palaeozoic. In California it is amply proved 
by rare but characteristic fossils that the gold-bearing sedimentary rocks are Mesozoic. Generalizations similar to 
Murchison’s have been attempted with reference to ores of other metals, but the simple fact seems to be that 
eruptive activity or metamorphism is usually a concomitant of the concentration of ores in veins and other allied 
deposits, and that the older the rocks the greater the general probability that they will have been subjected to 
action of this description. Iu the search for coal the fact that the important deposits of the best character are 
confined to one formation has been of great economical value. The geological indications accompanying the 
occurrence of veins are to be sought, not in the age of the rocks, but in evidences of disturbance and of certain kinds 
of decomposition of the surrounding country. The decomposition or alteration of rocks in the neighborhood of ore 
deposits has been but little studied by geologists until lately, for very sufficient reasons; but of the fact of a 
connection between it and the deposition of ore California affords excellent examples. The “bed-rock” or 
auriferous slates of the gold belt is characteristically altered, and the metamorphic stratum in which cinnabar occurs 
are at once recognized by those familiar with them as “quicksilver rock”. 

The belt of metamorphic rocks which incloses the greater part of the gold-quartz veins of California is insignificant 
in width and of little industrial importance south of the southern boundary of Mariposa county. To the north of 
that line, however, it suddenly widens. Passing northward, the breadth of the l>elt is stated at about 25 miles 
hi Tuolumne county, 24 miles in Calaveras, 12 in Amador, and 30 in El Dorado. In Placer it is not well exposed, 
being covered by gravel and volcanic rocks. North of Placer county the metamorphics occupy most of the western 
slope of the range for a considerable distance, with occasional irregularly distributed patches of granite, but in 
Butte county the edge of the great lava fields, which occupy much of the surface of northeastern California, are 
encountered, and cut off the central mining region. The same gold-bearing series seems to reappear in the north¬ 
western counties, but its character and relations are less well understood, and its industrial importance is smaller 
than in central California. 

As illustrative of the structure of the gold belt, Professor Whitney describes iu some detail the important 
portion lying between the Merced and the Stanislaus rivers. Starting from the west, or at the bottom of the Sierra, 
the first rock encountered is horizontally stratified and undisturbed Tertiary sandstone. To this succeeds the belt 
of Mesozoic metamorphics in nearly vertical strata. The lower edge is composed of talcose and chloritic slates, 
weathering irregularly, and locally known as u grave stone ” slates. Next comes a wide belt of a dark-grayish 
green, somewhat porpliyritic, material, which shows a sheeted structure, though not the tine lamination of clay 
slates. This was known to the state survey as “ porpliyritic green slate”, but Professor Whitney and Mr. 
Wadsworth are inclined to regard it as a metamorphosed diabasitic tufa. This belt incloses another of argillaceous 
slate, carrying Jurassic fossils, with which is associated the “mother lode”, or the “great quartz vein”. 
Accompanying the argillaceous slate and the mother lode is a band of serpentine, (a) In the southern portion of this 
section the serpentine is confined to the northeast side of the argillaceous slate, but near the Stanislaus river it 
widens out, occurring in irregular patches and on both sides of the slates. 

The strike of the metamorphosed rocks is, as a whole, parallel to the trend of the Sierra, but there are many 
sharp deflections. The dip of the slates in the southern and central portion of the gold belt is nearly vertical, and 
usually to the northeast; but in the northern portion, where the belt widens out, the dip becomes irregular, and over 
wide areas is to the west, becoming flatter as the distance from the crest of the range increases. 

Though not confined to the argillaceous slates, or even to the metamorphic strata, the gold-quartz veins of 
California are more frequent and richer in the argillaceous slates than elsewhere, many fine veins beside the 
“mother lode” occurring in it. The veins are usually parallel to the stratification, as the following quotation 
shows: ( b) 

A very heavy quartz vein passes a little south of Big Oak Flat, Tuolumne county, cutting the strata of slate in which it is 
contained at a small angle, the lines of bedding of the wall-rock appearing to run nearly northwest and southeast, while the vein of 
quartz has a strike of N. 30° \V.; it dips to the east at an angle of 30°, the slates themselves standing nearly vertical. This is, perhaps 
the most marked instance hitherto observed in the state of a heavy quartz vein differing essentially both in dip and strike from the 
inclosing rocks. 


a The origin of serpentine is a disputed point. If it is a fact, as eminefrt mineralogists have maintained, tha t it occurs as an alteration 
of hornblende and pyroxene as well as of olivine, there appears to be no difficulty in accounting for its presence in metamorphic rooks. 
Chlorite and serpentine, however, are occasionally confounded. 
b Geological Survey of California : Geology, vol I, p. 237. 





10 


PRECIOUS METALS. 


The most remarkable primary metalliferous deposit of California is the mother lode already referred to. Many 
of the great mines of the state are upon it, and others are in its immediate vicinity on veins which most likely have 
an intimate structural connection with -it. It extends from a point a few miles southeast of the Merced river, in 
Mariposa county, to near the center of Amador, a distance of about 80 miles. Though the croppings are in places 
hidden by overlying rock or detritus, they are visible for a great portion of the distance at such frequent intervals 
that the identity of the lode is not doubtful. It is more than probable that it extends to the north of the point 
indicated, but it cannot be traced with absolute certainty. 

This powerful lode (a) is made up of irregularly parallel plates of white compact quartz and crystalline dolomite or magnesite (b) 
more or less mixed with green talc; and these plates, which somewhat resemble the “combs” of ordinary lodes, are either in contact or 
separated from each other by intercalated layers of talcose slate. The quartz is chiefly developed in the central portion of the vein; and, 
from its color and resistance to decomposition, it gives rise to a very conspicuous outcrop, forming the crest of the hills, so that it can be 
readily seen from a distance of several miles. The dolomitic or magnesitic portion decomposes some what-readily, and it becomes a kind 
of 1 ‘ gossan * or cellular, ferruginous mass, of a dark-brown color, often traversed in every direction by seams of white quartz. The quartz 
is the auriferous portion of the lode, although it is far from being uniformly impregnated with gold. Most of the mines which have beeu 
worked between the Merced and the Stanislaus are on the northeast side of the great quartz vein, either in contact with it or in some 
parallel band of quartz subordinate to or at a little distance from it. The talcose-slate bands in the vein are often themselves more or 
less auriferous. 

Professor Whitney does not regard it as by any means proved to be a fissure vein, or even an exclusively 
segregated one; on the contrary, it seems to him most likely the result of metamorphic action on a belt of rock of 
peculiar composition, and perhaps originally largely dolomitic in character. 

Besides the quartz veins in the metamorphics of California, there are also many in the granites of the same 
region. Though of less importance than those in the sedimentary rocks, many of them have been worked with 
profit, but no careful comparison has been instituted between the two classes of veins. In some instances at least, 
and when near the slates, the veins in the granite are parallel to the stratification of the metamorphic rocks, and 
are also essentially gold Veins.,. It is probable, however, that on closer investigation they will be found to present 
characteristic differences. , 

Gold never occurs in nature unassociated with silver, and silver, it is said, is never wholly free from gold; but 
there seems, nevertheless, to be a natural distinction between gold veins and silver veins. In Nevada, Arizona, 
and throughout Mexico gold usually occurs only in minute particles entangled in sulpho-salts of silver and other 
metals, except near the surface, where atmospheric action has decomposed the original matrix. Though the value 
of the gold in such cases sometimes equals or exceeds that of the accompanying silver, the latter usually greatly 
surpasses it in weight. In the gold belt of California, on the other hand, the gold occurs in great part as flakes or 
even as masses, often not immediately in contact with sulphides, and carrying in alloy only 0.100 or 0.200 of 
metallic silver. As a rule, the gold does not assume a crystalline form in the California mines, but more or less 
perfect octohedral forms have been found at Spanish Dry Diggings and at Byrd’s valley. ' Cubical crystals have 
uot until lately been observed, and Professor Whitney notes that he has neither seen nor heard of any in the state, (c) 

Sulphides always accompany the gold in the veins, though these minerals are not always found in contact with 
the larger particles of the metal. So general is the association, however, that when, as is often the case even with 
rich quartz, the gold is not visible to the naked eye, miners judge of the value of the ore by the quantity of 
sulphurets. Quartz with plenty of sulphurets and no visible gold often occurs in large bodies, and is apt to pay 
better in the long run than ore with very coarse gold, or “ specimen quartz”, as it is called by the miners. The 
minerals embraced under the term “sulphurets” are considerable in number, but the most common are pyrite, 
mispickel, zincblende, and galena. Though seldom containing the greater part of the gold, it is rarely that the 
sulphurets do not include a portion of the metal in such a way that it canpot be extracted by amalgamation. 
Concentration of the sulphurets, followed by chloridation, is then the readiest means of extraction. There is an 
occurrence of cinnabar in gold quartz veins inclosed in slate in Calaveras and one in Mariposa. 

The distribution of gold in the veins is usually very irregular, and while on some veins it will pay to extract 
the ore from wall to wall, in most cases certain belts or chimneys of rock only are remunerative. 

Had the veins been deposited in the slates before they were raised into their present position in post Jurassic 
times, they must have been much faulted and broken. This is not the case, nor is it probable that veius could 
have formed in undisturbed strata. On the other hand, there can be no doubt that the auriferous gravels have 
been formed at the expense of eroded croppings of the quartz veins; and the veins, or most of them, must therefore 
have been deposited before the gravels. These, according to Professor Whitney, were accumulated during the whole 
of the Tertiary period, while Cretaceous gravels appear to be entirely absent. The range was above water during 

a Professor Whitney: Auriferous Gravels, p. 46. 

b In the only specimen which has thus far been chemically examined the supposed dolomitic portion proves to be an intimate mixture 
of quartz and magnesite. 

c In December, 1882, however, Mr. James Terry purchased a specimen of gold from Louis Abraham, Kearney street, San Francisco 
which is said to have come from Eldorado county, between Plumas and Placerville, which Bhows a number of fine cubical crystals with 
full faces and sharp edges. The same specimen also shows well-developed dodecahedrons, trapezohedrons combined with the cube and 
octohedron, a cube the comers of which are truncated by a trapezohedron, and possibly other combinations. 





GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


11 


the Cretaceous, aud such fresh-water deposits as accumulated ou its west slope seem to have been swept away 
during the succeeding period. The natural inference would seem to be that the formation of the veins occurred 
between the end of the Jurassic and the beginning of the Tertiary, and that it was intimately connected with the 
upheaval of the Sierra and the metamorphism of the strata of preceding epochs. 

Substantially coincident with the area of gold veins is that of the auriferous gravels of California. In the 
gold-bearing regions of all countries secondary deposits of the metal, associated with gravel or sand, have played a 
large part, because the gold may be separated from such loose material at a low cost. In California, however, the 
gravels have proved particularly important because of the invention and development there of the peculiar system 
of hydraulic mining, which consists in washing the gravels into sluices provided with quicksilver by the aid 
of powerful jets of water. The great importance of this system is due to the fact that it is among the least 
costly methods of handling material, if it is not the very cheapest known. It costs under favorable circumstances 
but five cents per cubic yard, or, say, three cents per ton, aud sometimes even less. It thus renders deposits 
of gravel valuable which under most conditions would be absolutely worthless. Several conditions, however, are 
necessary to the successful prosecution of hydraulic mining, among which the most important are a deep gravel 
bank, abundance of water with a great head, and some available valley at a lower level than the bank, into which ^ 
the gravel from which the gold has been extracted may be washed.- The topographical and climatic conditions in 
the Sierra are peculiarly favorable for this process, while in Australia, where gravel is abundant, circumstances 
rarely permit the application of this method of extraction. 

The gravel consists of bowlders and pebbles of various rocks, with silt, clay, and volcanic ash. The gold occurs 
as nuggets and fine particles, free or nearly free from rock, but also as fragments of gold quartz, and is accompanied 
by a variety of other heavy substances, as magnetite, garnet, and zircon; rarely and locally also by cinnabar, 
platinum aud iridosmine, diamonds, native copper, and other substauces of high specific gravity. One of the striking 
features of most deep gravel banks is the so-called “blue lead”. This name is applied to the lower portions 
of banks, which are generally somewhat closely compacted and possess the color of the blue clays occurring all over 
the world. Although the “ blue lead” has led to wholly untenable theories as to the character of the gravel deposits, 
its nature is very readily accounted for. Loose materials near the earth’s surface are every where impregnated with 
a small amount of organic matter carried down from the surface by water and filtered from it by the porous strata. 
This organic matter, in the absence of free oxygen, exercises a slow but inevitable reducing action ou ferric oxide 
and on some ferric compounds, and gives the soil the bluish color characteristic of the presence of iron in the 
ferrous state. Close to the surface, however, oxygen, either gaseous or in aqueous solution, more than counterbalances 
the reducing action of the organic matter, and above a certain line the gravel is consequently reddened by ferric 
oxide. In shallow deposits the gravel is usually reddened to the bottom, but of course this does not necessarily 
imply that such gravels have a different, origin from those of a bluish tint. 

To a very large extent the deep gravels are covered by a capping of volcanic material, sometimes as solid black 
basalt, and sometimes as loose volcanic “ ash”; and while some banks are not thus covered, these are rarely at any 
great distance from volcanic capping. The volcanic material has protected the gravels in many cases from erosion, 
but there is also a connection in their deposition. The gravels occur in ancient river beds, which formed the natural 
channels for the flow of lava as well as of water. Volcanic eruptions occurred during the period of the gravel 
formation, as well as at its close, and sheets of ash or even of solid lava are found in the banks as well as upon 
them. When the lava cap is thick and solid the gravels can only be mined by drifting, and are not workable by 
the hydraulic process. 

Besides the deep gravels, which date from a period prior to the volcanic eruptions, there are many accumulations 
of recent origin. 'The bars of the present river system have yielded great quantities of gold, and there are many 
shallow placer deposits which are no doubt due to the modern erosion of quartz cropping^ while others are a 
consequence of the erosion of older gravels. The modern gravels, however, are trifling in quantity as compared 
with the older deposits. Some of the shallow placers are no doubt mere remnants of deeper Tertiary gravels which 
have not been wholly carried away by the erosion of the present epoch. 

The bed-rock of the gravel deposits varies in character, being either limestone, granite, or inetamorphic slate; 
but the last is the rule, and few important deposits occur far from the slate bed-rock, which, as has been explained, 
is the main, though not the exclusive, habitat of the gold veins. In nearly all cases the gravel rests in local 
depressions, early recognized by the California miners as the beds of former streams. Many of the gravels, it is 
true, are high above the present drainage system, and even form the tops of hills; but this is due to the erosion of 
the present stream-beds, which have been cut down to a great depth since the gravel period. The bed-rock is 
usually rough, consisting of nearly vertical slates, and the natural crevices, or “ riffles”, large and small, thus Formed 
often contain extremely rich gravel. As might naturally be supposed, the greater part of the gold is generally 
found near the bed-rock, for as gold is about seven times as heavy as ordinary rock every disturbance of a gravel 
bar in a stream tends to shift the gold to a lower level. Sometimes, however, rich gravel is again deposited over a 
comparatively firm stratum in the gravel, and occasionally gold is quite uniformly disseminated through a whole 
bank. 


12 


PRECIOUS METALS. 


An idea has been current in the mining region that by some process masses of gold in the gravel have increased 
in size. For this there is absolutely no valid evidence. The rounded masses ol gold found could not have been 
deposited from solution in that form oi^ith such a surface. They have been beaten and worn into shape, much as 
the accompanying pebbles have beenwormed, the only difference being due to the fact that gold is malleable. 
Professor Whitney believes it probable that the higher croppings of the gold veins were richer and contained larger 
masses of gold than the lower portions of the veins still in place, and it there was any difference at all it was 
probably of that character. As Professor Newberry (a) points out, however, the gravels represent vastly more 
vein-quartz than has been extracted by deep mining, and the proportion ot large masses of gold met with in the 
veins probably bears as great a ratio to the total weight of quartz extracted, as do the nuggets in the gravels to the 
quartz from which their metallic contents were derived. 

The investigations of the state survey have shown that the deep gravels were deposited by rivers which 
headed in the high Sierra and ran in a westerly direction, emptying into the sea, which, in Tertiary time, occupied 
the great valley of California. Although all the details of the former river system cannot now be traced out, the 
courses and relations of the channels developed by hydraulic mining seem to establish this point beyond a question. 

-There were two great rivers in the Pliocene epoch, one corresponding to the American and the other to the Yuba; 
but the Bear river of that time probably emptied into the American at a considerable height above the valley. 

The gravels cannot possibly have accumulated under the present conditions of precipitation. A far greater 
erosive power than that exhibited by the California streams of to-day must have been exerted at the time in 
question, as no one can doubt who has ever visited the gold belt. For a long time past the present rivers have 
merely been deepening their narrow courses, and when freshets occur they merely serve to sweep the caiions clear 
of debris, but cannot alter the course of the stream. The width of the old channels, as well as the character of 
the deposits, shows that the old rivers were tumultuous streams of great volume, which frequently burst their bounds 


and formed new beds. 

The evidence of enormous erosive power during the deposition of the gravel has been so apparent to all 
observers that some of them have called in the action of great glaciers to account for the occurrence of the deposits. 
According to Professor Whitney this is incorrect; indeed, he holds that the former glaciers of the Sierra did not 
come into existence until after the greater part of the gravels occupied their present position. The bed-rock which 
the gravels cover, and which they have protected not only from erosion but even from atmospheric action, shows 
no traces of glacial polishing and scratching. This is in marked contrast to the higher regions of the range, where 
the glacial markings are almost as fresh as in the Alps. Nor are occurrences frequent which can possibly be 
confounded with moraines, while the fossils found indicate, according to Mr. Lesquereux, a climate a few degrees 
warmer than that of the present time. 

Professor Whitney believes the great precipitation necessary to account for the large rivers of the Tertiary in 
California to have been mainly due to the prevalence of higher temperatures at that period and to the accompanyi .g 
increased evaporation from the surface of the ocean. It is at least conceivable that the climate should have been 
something like that of the Khassia hills, upon parts of which the hot winds from the bay of Bengal deposit some 
500 inches of rain yearly. The presence of a sea at the foot of the range must have largely increased the rainfall, 
as has been pointed out. It is to be inferred from Professor Whitney’s remarks that he supposes the climate of 
the Sierra to have been too warm for glaciers during the Tertiary. He regards the present climate, on the other 
hand, as too dry to permit of their formation, though there can be no doubt.of their existence in the higher part of 
the range above the gold belt up to within a comparatively short time. A few small glaciers on the northern 
slopes of mount Shasta are now the only remnant of the former ice system of the state. The Sierra glaciers were 
of the mountain type, however, comparable at their greatest extension with those of moderiP Switzerland, and 
nothing like a general glaciation or a diluvial period ever existed in California. 

The following sections of auriferous gravel deposits are selected from a large number furnished by the reports 
ot the special experts to illustrate the mode of occurrence of the gravels in various portions of the state : 


BONANZA MINE. 

MOKELUMXE HILL DISTRICT, CALAVERAS COUNTY, CALIFORNIA. 


I 

II 

III 

IV 

Lava cap in places. 

Alternating fine and coarse sand with pebbles (chiefly quartz) 

Cement. A quartzose (also granitic and slaty) conglomerate, cemented with 
sesquioxide of iron. 

Bed-rock, slate. 

| Maximum, 125 feet; average, 75feet. j 

Richest portion usually lower 15 
feet above bed-rock. In places 
gold nearly evenly disseminated 
throughout deposit. 

The ancient channel on which this mine is located is traceable, with intermittent breaks, for 10 miles. The channel is 500 feet wide, the outer edges barren, 
and the pay channel is 300 feet wide. 


a School of Mines Quarterly, November, 1881. 

































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


13 


LAGRANGE HYDRAULIC MINE. 

LAGRANGE DISTRICT, STANISLAUS COUNTY, CALIFORNIA. 


I 

• 

Red sand. 




II 

Coarse red gravel, containing pebbles of granite, etc. 




m 

Red cement (“hard-pan ’’). 




IV 

White siliceous clay. 




V 

Red cement (same as HI)... 


■ Maximum, 300 feet; average, 40 feet 


VI 

Sand with pebbles. ... 




VII 

Loose yellow sand. 




VIII 

Dark-colored gravel, containing debris of granite, argillaceous slate, “ ser- 



Lowest 6 feet 8 inches richest 


pontine," etc., with some quartz. 




IX 

Bed-rock at Lagrange v diorite and slate”; at Patricksville "basaltic tufa” 




(no specimen). 

I 



Quartz forma but a small proportion of the gravel, which is chiefly granite, etc. Generally the upper workings do not pay, 90 per cent, of the gold being 
obtained from near tbe bed-rock ; but sometimes the upper horizon is the richest. At Patricksvillo, gravel is overlaid by tufa ; not much tufaeeous cropping at 
Lagrange. Ancient river bed. Deposit in patches for 1 mile wide by 2£ miles long. 


LYON DRIFT MINE. 

PLACERVHLE DISTRICT, EL DORADO COUNTY, CALIFORNIA. 


Mr 


I 

, “ Lava ” or a consolidated sediment of volcanic origin. 

60-130 feet. 

II 

Mountain gravel. 

0-50 feet. 

HI 

Granitic sand, in places consolidated. 

0-20 feet 

IV 


Maximum, 20 feet; average, 3J feet. 

V 

Bed-rock, slate. 


Three benches of ancient river, overlaid with volcanic matter, 60 to 130 feet wide, are here traceable for 3,000 feet. 

ORION MINE. 

IOWA HILL, PLACER COUNTY. CALIFORNIA. 


I 

II 

III 

Sand and fine gravel.... i 

Coarser blue gravel.*. j 

Bed-rock, black slate, rough. 

| Maximum, 180 feet; average,100 feet. | 

All pays. Richest near bed-rock. 

No lava; no quicksand. Ancient river bed, said to be 2,000 feet wide, traceable 2J miles. 

VAN EMMONDS’ MINE. 

MICHIGAN BLUFFS, PLACER COUNTY, CALIFORNIA. 

I 

II 

III 

IV 

V 

• 

Very little lava. 

Fine gravel, alternating with sand strata. 

Blue gravel. 

White gravel. 

Bed-rock, rough slate. 

1 f 

} Maximum, 50 feet; average, 30 feet. <( 

J ’ l 

All pays; but white gravel nearest 
bed-rock best 

Petrified wood, leaves of oak, pine, etc., found in sand strata. It is unusual to meet white gravel beneath the blue. 

MORRIS RAVINE MINE. 

MORRIS RAVINE DISTRICT. BUTTE COUNTY, CALIFORNIA. 

IV 

V 

Hard, solid lava cap in places. 

Fine quartz gravel. . 

Rotten bowlders. 

( age. 40 feet, 1 

3-20 feet. .1 [ 

A little gold throughout. Blue gravel 
richest. 

B ed-rock, chloritic and clay slates, rough and decomposed. 


Pipe-clay occurs irregularly throughout deposit. Quicksand met with. 

SPRING VALLEY MINE. 

CHEROKEE DISTRICT. BUTTE COUNTY, CALIFORNIA. 


I Lava cap over part of claim. 

II | Fine quartz gravel.. ! 

III | Rotten bowlders of yellow slate mixed with quartz gravel.. 

IV Blue gravel. .. 

V Bedrock, where exposed, described as basalt” like tbe cap, probably 
metamorphic. Surrounding country r ock is slate. 

Water and quicksand found in large quantities at the depth of 300 feet. Barren pipe-clay, 25 to 150 feet in places, as a rule overlying rich gravel. 


25-150 feet. | 
5-15 feet. 

i sn fppt/ 


1 

Maximum depth, 400 l 
feet; average, 200 feet, j 


Best pay in III and IV on bed-rock. 




















































































































14 


PRECIOUS METALS. 


HUNGARIAN HILL MINE. 

PLUMAS COUNTY, CALIFORNIA. 


I 

II 

in 


. .i > Maximum, 110 feet; average, 75 feet. 

Loose gravel, same character from surface to bed-rock .I > 

Generally soft slate bed-rock; in places hard siliceous slate. Rough, with j 
projecting points in some places rising nearly to surface. 


River lied, with rim-rock on each side, 250 feet wide; traceable, 3J miles. No lava, water, or quicksand. 


Gold throughout gravel. All pays. 


CARROLL DRIFT MINE. 

McADAM’S CREEK DISTRICT, SISKIYOU COUNTY, CALIFORNIA. 


I 

II 

III 

IV 
V 

VI 

VII 

vm 


Loam. I feet. 

Loose tailings.. 0 feet. 

Wash gravel, with clay and sand. 10 feet. 

Compact yellowish-white clay (water level). j 18 inches to 4 feet. 

Coarse yellowish gravel (bulk of deposit).. . 

Quartzose matter. 3-6 inches. 

Greenish gravel. 

Bed-rock, rotten brown slate and hard fine-grained blue slate. 


I 

I 

l Maximum, 115 
feet; average 
73 feet. 


None barren, but only a small portion 
pays for drifting. The pay streak 
is 200 feet wide and length of claim. 


Bed of McAdam's creek. Miuing is carried on over a length of 3J miles by a width of 150 to 600 feet. 


Good (iay. 

12 feet.. Best pay on bed-rock and in bed-rock 

I to a depth of 2 feet. 


OAK GROVE DRIFT MINE. 

McADAMS CREEK DISTRICT, SISKIYOU COUNTY, CALIFORNIA. 


I 

Loam. 

4 feet. 



II 

Loose tailings. 

6 feet. 



III 

Wash gravel, with clay and sand.. 

10 feet. 

, Average, 65 feet. 

None of the gravel is barren. 

IV 

Compact yellowish clay (water level). 

18 inches to 4 feet. 



V 





VI 

Quartzose matter. . 

4 to 6 inches. 


Good pay. 

VII 

Yellow gravel. 


The best pay is 1 to 3 feet on bed-rock 

VIII 

Bed-rock, brown slate, ridgy and seamy in places; in others soft and open. 


and 1 to 3 feet in bed-rock. 


PACIFIC MINE. 

HUMBUG DISTRICT, SISKIYOU COUNTY, CALIFORNIA. 

1 j Loose wash gravel.. 

II Coarse yellow gravel, containing many large bowlders 

III j Fine sand.. 

IV I Yellow gravel. 

V ; Dark yellow gravel... 

VI j Blno gravel. 

VII Bed-rock, blue slate. 


River bed traced for 1 mile, average 50 feet wide. 

BUNKER HILL MINE. 

DEL NORTE COUNTY, CALIFORNIA. 


I 

Red loam mixed with fine gravel. 

15 feet. ] Maximum depth of bank, 125 
,r, ( feet; average, 80feet. Maxi- 
( mum depth of gravel, 50 feet; 
20 feet, j average, 30 feet. 

"J 

II 

Loose gravel. 

1 None of the gravel is barren, but the 

III 

Gray cement streak, 60 feet wide, Large bowlders in best ground. 

( richer portion is near bed-rock. 

IV 

"Serpentine” bed-rock easily piped, having blue slate under it (Leavens). 
Specimen determined as highly metamorphic dioritic-looking rock. 



Channel one-half to three-quarters of a mile, 150 feet long; course a little west of north. 


5 feet. 

8 feet. 

6 inches to 2 feet. 
20 feet. 

1 foot. 

8 inches to 10 feet. 


I Maximum, 50 feet; 
average, 45 feet. 


Contains but little gold. 


> N one barren. 


■ Best pay. 


Large deposits of copper ores have been found in the auriferous slate series, especially in Calaveras county, 
Copperopolis is the principal point, but there are a'so deposits at Campo Seco, and again further north near lone 
City. Prospects have also been found on the same line beyond this point. The or«s are native copper and carbonates 
near the surface, replaced by a mixture of iron and copper pyrite below the water-line. The deposits have the same 
dip and strike as the inclosing cliloritic slates. Extensive shipments were made in former years. 

Mono and Inyo counties, though politically united to California, considered from a pliysico-geographical point 
ol view, form a portion ot the Great Basin. I he sedimentary rocks of Mono county appear to be Mesozoic, but the 
western edge ol the great Palaeozoic area which covers the eastern portion of the Great Basin crosses the California 
line about due south ot Columbus, Nevada, passing near Owen’s lake and then diverging to the southeast. Great 
Quantities of lava are met ith in both counties, as throughout the Great Basin. The deposits of these counties also 








































































































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


J 5 


bear a much closer resemblance to those of Nevada than to those of central California. The best known mining 
localities are Bodie, Cerro Gordo, and Panamint, but none of them have formed the subject of any detailed geological 
investigation. 

The bullion of Bodie is usually regarded as gold, because its silver contents are much less valuable than the 
accompanying gold. Reports made to the director of the mint for the year 1880 show that from 5 to 63 per cent, 
of the value of the bullion produced by the various mines was silver, which also formed 17.01 percent, of the value 
of the total product ($3,063,690 13). It follows that from 45.7 to 96.5 per cent, of the weight of the bullion from 
different mines and 77.72 per cent, of the total weight was silver. Jn 1879, when a smaller portion of the colorados 
w'ere worked out, silver only formed 65.2 per cent, of the entire weight. Bodie metal may therefore very properly 
be regarded as a highly dore silver bullion, similar to that of the Comstock lode, and as essentially different from 
that of the gravel and slate region ordinarily known as the gold belt. 

The Comstock was at first worked for gold. The Bulvver, the Syndicate, and the Standard Consolidated, which 
show but little silver, are on top of a hill where the water-level is far from the surface and the quartz is reddened 
to a great depth ; the Bodie Consolidated, Noonday, and others are at low^er elevations. The sulphurets of these 
mines are not oxidized, and the bullion shows a large amount of silver. 

The gangue minerals of these deposits are base sulphurets, quartz, and calc-spar. They are inclosed in extremely 
decomposed rock, bearing clear signs of solfataric action. The rock is so highly altered that tolerably fresh 
specimens are not obtainable near the mines. Slides of the freshest specimens collected are not decisive as to the 
character of the rock. They show plagioclase, and apparently some orthoclase, accompanied by mica and a little 
hornblende; the ground mass also contains quartz. Only a detailed examination in the field will decide what name 
the rock should bear. 

The mines of Cerro Gordo were not in operation during the census year. The deposits, which at one time were 
very productive, were masses of argentiferous lead ores occurring in limestone, and consisting for the most part of 
carbonate, sulphate, and other decomposition products of galena. Schists and slates were also met with in the mines, as 
well as a granite-porphyry. This is said to occur as a dike in the Union mine and elsewhere, and is locally called syeuite, 
though it is quartzose and micaceous. Panamint was for a short time a very nourishing camp, its prosperity 
being derived from veins in limestone carrying chiefly argentiferous gray copper ore or freibergite, associated with 
galena and zincblende. Mining is still being carried on, but the richer deposits were soon worked out. The age of 
the limestones of Cerro Gordo and Panamint is unknown. Both districts lie near the contact between the Palaeozoic 
and the Mesozoic, and may belong to either; but limestones are exceptional in the Trias and Jura of the Sierra region, 
while they predominate in the Palaeozoic area. 

Gold has been found at a great number of points in the Coast ranges proper and in the western ranges of 
southern California. No doubt large individual profits have been made at certain localities, and it is by no means 
impossible that as good or better veins than those found await discovery. It is scarcely likely, however, that after 
thirty years of skillful prospecting any important gold-mining region has escaped observation. A few years since 
great hopes were raised by the prospects on veins in the slates and on the contact between slates and granite in 
the Julian and Banner districts near San Diego, but they have fallen short of the expectations excited. 

The so-called Gold Bluffs along the coast of the northern counties, especially near the mouth of the Klamath 
river, are bluff's which contain extremely small quantities of gold, and seem to be beds of detritus left by the 
shifting of the river channels. The sea encroaches upon them, and when the surf strikes the beach in certain 
directions and with a certain strength the gold is concentrated in comparatively rich sands, which are gathered 
and treated in apparatus of various designs by amalgamation. 

The only quicksilver ore of great importance is cinnabar, although metacinnabarite, the black sulphide, is 
rather abundant in a few-mines, and metallic quicksilver sometimes accompanies the deposits of its compounds. 
The metacinnabarite described by Dr. G. E. Moore was amorphous, but according to Mr. Goodyear it also occurs 
as minute crystals. Cinnabar is found in a great number of localities in the Coast ranges for 100 or 150 miles north 
and south of San Francisco, always, so far as known, in metamorphic rocks of Cretaceous age. The character of 
the metamorpliism is generally peculiar, and the so-called quicksilver rock is readily recognizable. It is asilicified 
chert like material, often reddened by iron oxide, and usually accompanied by serpentine or serpentinoid matter. 
In almost all cases pyrite or marcasite and bituminous matter accompany the cinnabar, and mispickel and copper 
pyrite are reported in a few instances. At Sulphur Banks, on Clear lake, native sulphur occurs in great quantities 
with the quicksilver ore, and native gold has been found in water-worn masses of cinnabar not far from the same 
locality. The converse occurrence of cinnabar in two of the quartz veins of the Sierra gold belt has already been 
noticed. Stibnite is reported as occurring with cinnabar at the Lake mine near Knoxville. The usual gangue 
minerals are quartz, caleite, and magnesite. 

Cinnabar does not occur in well-marked veins, but generally in irregular bodies distributed through the rock. 
In the New Almaden mine, which has been much more extensively woiked than any other in the state, these bodies 
appear, from a model constructed by the owners, to lie on a curved surface, indicating a geometrical relation between 
the positions of the several ore-bodies, though an obscure one. At this mine the masses of ore are usually connected 
by tiny seams of the same material. There is a strong similarity between this mode of occurrence and that of 
many lead ore deposits in limestone, and it may be that the problem of their true character is the same. 


16 


PRECIOUS METALS. 


The quicksilver country north of San Francisco is a volcanic region, while to the south volcanic rocks are 
subordinate in some localities and wanting in others. To the south, too, there is no indication of any recent 
deposition of the ore, while to the north deposition is still actually in progress. No general inference as to the 
genesis or the age of the deposits can therefore be drawn without further investigation, while the great similarity 
in the association of minerals suggests a similar origin for most of them. 

The Sulphur Banks, on Clear lake, forms the subject of a recent paper by Professors Le Conte and llisiug. (a) 
At that point cinnabar with pyrite and some bituminous matter, as well'as free sulphur, is now being deposited. 
The hot waters rising to the surface are charged with sulphides of ammonium and of the fixed alkalies, and appear 
to carry in solution cinnabar and pyrite, which are deposited, in the opinion of the authors, by reduction of 
temperature and pressure, probably assisted by neutralization through the percolation of free sulphuric acid from 
the surface. The deposition of sulphur is a surface phenomenon, it may also have attended the formation of the 
deposits to the south of San Francisco and have been subsequently removed by erosion. 

The only Californian coal-fields of great importance are those near Monte Diablo, which occur in sandstones of 
the Upper Cretaceous or Tejon group. According to Professor S. F. Peckham’s examination, ( b) these coals carry 
from 5 to 11 per cent, of ash, 4.} to 5£ per cent, of sulphur, and from 11£ to 13 per cent, of water. The refuse dumps 
of these mines frequently take fire spontaneously from the oxidation of pyrite. Coal of the same age occurs under 
less favorable conditions at Corral Hollow, in the Monte Diablo range. Seams are found here and there all along 
the Coast ranges, but they are usually thin, and even when of a workable thickness are so faulted and broken as 
to be of small value. 

Lignite of Pliocene age is found at lone valley, Amador county, and is used along the line of the railroad to 
some extent at Dog creek, near the Truckee river. 

In southern California there are vast quantities of bitumen, from which asphalt and a certain quantity of 
illuminating oils are obtained. The bitumen occurs in shales of the Miocene, which are in large part too much 
disturbed to permit of the accumulation of pressure necessary to induce fiowing wells. Many of these bitumens, 
though thin as they issue from the ground, oxidize and are converted into hard asphalts. According to Professor 
Peckham, the California bitumens are composed of a different series of hydrocarbons from those which make up 
the petroleums of Pennsylvania, 

AMADOR COUNTY. 

This county lies directly across the main gold belt. Quartz mining takes the first rank, though there are gravel 
deposits, and hydraulic mining is carried on to a considerable extent. The gold in the veins is associated with iron 
and copper pyrite, mareasite, mispickel, and .small quantities of galena. Thegangue is chiefly quartz, but some 
calcitc is occasionally found in the veins. The country rocks are slate and granite, the former being predominant, 
but a greenstone also occurs, which, though much decomposed, is probably a diabase or proterobase. The mother 
lode has been traced with certainty from Mariposa to about the center of Amador. Copper is found in the western 
portion of the county, but it is not at present worked, and a lignite occurs at lone City which is of considerable 
local importance. 

AMADOR. 


[Note.— Determinations in parentheses are given oq theanthority of the experts.] 




WALLS. 


Mine. 

Ore and gangue. 



Character of 

Foot. 

Hanging. 

deposit. 

AMADOU CITY. 





Keystone. 

(Gold, ohalcopyrite, galena), pyrite and quartz. 

Proterobase (?) *. 

Proterobase (?)*. 

Vein. 

JACKSON. 





Monte Richard. 

(Gold), iron-stained quartz. 

(Greenstone or augite-por- 
phyry, called granite ) 


Vein. 



Oneida. 

(Gold, galena, ohalcopyrite, and mareasite). pyrite 
and quartz. 

Greenut one, probably an au- 
gite-porphyry. 

.'...do . 

Do. 



Zeile. 

(Gold, pyrite, rarely galena and ohalcopyrite, quartz). 

(?). 


Do. 

PLYMOUTH. 



Pacific Mining Company 
(Empire, etc., mines). 

(Gold), indeterminable black sulphurets and quartz .. 



Vein. 





8UTTEK CKEEK. 





Consolidated Amador. 

(Gold, galena, ohalcopyrite, mispickel), pyrite and 

(Clay mica slate).. 

(Talcoso 6late)_ 

Vein. 


quartz. 



VOLCANO. 





Madeira. 

(Gold), galena, calcite, and quartz. 

• 



* Examined microscopically. 


a American Journal , vol. 24, p. 23, 1882. 


b Geological Surveg of California: Geology, II, p. 44. 
























































GEOLOGICAL SKETCH OF THE PxYCIFIC DIVISION. 


17 


BUTTE COUNTY. 

A large part of Butte county lies in the Great Valley, and produces no gold$ but the eastern portion contains 
extensive gravel deposits, which are continuations of those of Plumas and Yuba. Much of the gravel is covered 
by a cap of basalt, and the bed-rock is, in all the cases reported, sandstone or metamorphic slate. 


BUTTE. 

[Note.—D eterminations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and ganguo. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

CENTERVILLE. 





Big Butte creek. 

(Gold gravel). 

(Sandstone)... 

Basalt cap *. 

Placer. 

CHEROKEE. 





(Gold gravel). 



Do. 






* Examined microscopically. 


CALAVERAS COUNTY. 

Both quartz and gravel mining are actively pursued in this county, which lies across the gold belt. The 
auriferous quartz carries iron and copper pyrites, mispickel, galena, and zincblende. The wall rocks in all the cases 
reported are metamorphic. The mother lode crosses this county. The gravel is of the ordinary character, and, 
as usual, is accompanied by more or less basaltic lava. Copper deposits occur below or to the west of the gold 
belt at and near Copperopolis. 

CALAVERAS. 

[Note. —Determinations in parentheses are given on the authority of the experts.] 


Mines. 

Ore and gangue. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

ANGEL’S. 

Gold, galena, and quartz. 



Vein. 

Do. 

MOKELUMNE HILL. 

Gwin. 

(Gold, mispickel, zincblende), pyrite, chalcopyrite, 
and quartz. 

(Black slate)..... 

(Black slate). 


DEL NORTE COUNTY. 

Auriferous gravels are the chief metalliferous deposits of this county, the bed-rock consisting of slate and 
other sedimentary strata. Beach sands are also worked to a small extent on the coast. 


DEL NORTE. 

[Note.—D eterminations in parentheses aro given on the authority of the expert.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 

Foot. 

Hanging. 

deposit. 


(Gold gravel). 

Metamorphic dioritic rock.. 


Placer. 



Schist and shale. 


Do. 



Slate.. 


Do. 





Do. 



Shale. 


Do. 


do. 

Slate. 


Do. 






VOL 13-2 








































































18 


PRECIOUS METALS. 


EL DORADO COUNTY. 

El Dorado lies across the gold belt, and contains a great deal of gold quartz, while the placers are comparatively 
insignificant. Some of them, however, buried under heavy caps of lava, are profitably worked, by drifting. The 
gold quartz carries the usual sulphurets, pyrites, mispickel, and zincblende. The country rock is chiefly slate. 
Copper ores also occur in the western part of the county. 

EL DORADO. 


[Note.—D eterminations in parentheses are given on the authority of the experts.) 


Mine. 

Ore and gangue. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

PLACERVILLE. 

(Gold gravel).. 

Slat© . 

Lava cap, basalt, pumice*.. 

(Greenstone and slate). 

(Slate)... 

Placer. 

Vein. 

Do. 

PlacerviUe. 

Springfield. 

(Gold, pyrite), talc and quartz. 

Gold, pyrite, mispickel, quartz, (zincblende and ga¬ 
lena). 

(Greenstone and slate). 

(Slate)... 





* Examined microscopically. 


FRESNO COUNTY. 

Fresno extends from the crest of the Sierra to the Coast ranges. It lies to the south of the main gold belt, but 
contains a few gold quartz veins in the Potter ridge district and elsewhere, carrying the usual sulphurets, and 
being inclosed in slates. At the western edge of the county is the famous New Idria quicksilver mine, in which 
cinnabar is accompanied by pyrite and bituminous matter. According to Mr. Goodyear, the ore does not occur in 
a vein, at least of the typical character, but in irregular bodies, distributed in metamorphic sandstone and shale. 

FRESNO. 


[Note. —Determinations in parentheses are given on the authority of the experts. J 


Mine. 

Ore and gangue. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

SAN CAELOS. 





New Idria. 

Cinnabar, (pyrite, chalcopyrite, and bitumen). 



Vein. 

POTTEE BIDGE. 

. 



Fresno Enterprise. 

(Gold, sulphurets, and quartz). 

(Slate) . 

(Slate) 

Do. 


• 




HUMBOLDT COUNTY. 

There is no gold quartz mining in Humboldt, and the placer mines are not extensive, compared with those of 
the central counties. The gravels appear to represent modern river bars of the Klamath, along the banks of which 
they are found, in some cases, however, at a very considerable elevation above the present stream. As in Del 
^soitc, there are auriferous beach sands, which can be worked with profit when certain combinations-of wind and 
waves have effected a preliminary concentration of the auriferous material. 

INYO COUNTY. 

The most important mines in this county carry argentiie’rous lead ores with calcareous gangue. They occur 
either in limestone or in limestone associated with granite and schist. The deposits are chimneys, or bodies of an 
irregular form, such as lead ores frequently assume elsewhere. Copper ores, associated with those of lead also 
occur. Where copper is the principal constituent the gangue is usually siliceous. The copper veins occur in 
limestone or in granite, or on the contact between the two. The lead ores are galena, cerussite, anglesite, and 
probably lead ocher, accompanied by argentite and other silver minerals. The copper ores are chalcopyrite, 
stromeyerite, tetrahedrite, bornite, and carbonates. They are usually argentiferous. In addition to the gangue 
minerals mentioned, fluorite is found in the Defiance mine, in a silver-lead deposit between granite and limestone. 
There are also gold-quartz veins in granite in the county, and some small gold placers. At the Lee mine argentite 
and horn-silver are reported as occurring in limestone. 




















































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


19 


INYO. 

I 

[Note.—D eterminations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 

Foot. 

Hanging. 

deposit. 

- CERRO GORDO. 

Ignacio. 



Schist (white limestone). 
Marble. 


J efferson. 




San Eelipe. 




Union Consolidated. 


5- d0 . X 

__do.. 

Vein. 

COSO. 

Defiance. 

Galena, cerussite, chalcopyrite, malachite, fluorspar, 
calcite, and pyrite. 

(Gold quartz). 

l Granite, porphyry dike*. ■> 



Josephine. 


♦ 

Do 

New Coso Company (includ¬ 
ing Lucky Jim and Christ¬ 
mas Gift). 

Mariposa... 

Galena, cerussite, calcite, and (anglosito). 

Granite. 

Limestone (containing bari¬ 
um). 

Do. 

(Gold, auriferous pyrite, and quartz!. 


Do. 





Phoenix. 




Bedded vein. 

Vein. 

KEAR8ABGE. 

Kearsarge. 

Cerussite, micaceous iron, limonite, (tetrahedrite, 
cerargyrite, and argentite), quartz. 

Stromeyerite, (tetrahedrite, galena, pyrite, and zinc- 
blende), quartz. 



PANAMINT. 

Hemlock. 


• 

LOOKOUT. 





Modoo Consolidated. 

RUSS. 

Brown Monster. 

(Cerussite, carrying gold and silver, with arsenic and 
antimony; caicito, iron oxide, and manganese min¬ 
erals.) 

(Cerussite, galena, bomite, malachite, pyrite, and 
quartz.) 

(White limestone). 

(Blue limestone). 

(Blue limestone). 

(Blue limestone). 

Bedded vein. 

Vein. 

FISH SPRINGS. 





Golden Wreath... 

(Gold, auriferous pyrites, and quartz). 

Granite. 



Alabama_____ 

(Gold quartz)... 

(Granite)... 

(Granite). 

Vein; also small 
placer. 

Deposits. 

Lee....... 

(Horn-silver, argentite, and quartz). 

(Limestone). 







* Examined microscopically. 


KERN COUNTY. 

Kern county lies south of the main gold belt; it nevertheless contains some gold-quartz veins in its northeastern 
portion, in the Sierra range, as well as some shallow placer gravels. 

LAKE COUNTY. 

The only important mineral deposits of Lake county are those of quicksilver, which occur at a number of points 
in considerable quantities, accompanied by pyrite, sulphur,bituminous matter, and quartz.* The inclosing rocks are 
metamorphic. The deposits are associated in some cases with basalt. 

LAKE. 


[Note.—D eterminations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 



Metamorphic. 

Metamorphic. 

Vein. 

EAST LAKE. 






(Cinnabar, native sulphur, bitumen, pyrite, borax, 

Sandstone and basalt. 

Sandstone and basalt. 

Irregular deposit. 


alum, and quartz.) 

. 

































































































20 


PRECIOUS METALS. 


LASSEN COUNTY. 

This county contains gold-quartz mines. The veins are associated with rocks which are in part metamorphic 
and probably also in part eruptive, but the specimens in the collection are so decomposed as to be indeterminable. 
Enormous quantities of lava cover much ground in this part of the state that would probably otherwise be 
remunerative. 

LASSEN. 


[Note.—D eterminations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

HAYDEN HILL. 

to 

Indeterminable. 

Indeterminable. 

Vein. 

Do. 



.. do. 







LOS ANGELES COUNTY. 

There is some silver mining in this county. Antimonial silver ores and argentiferous galena occur with pyrite, 
copper ores, and quartz inclosed between wall rocks which are chiefly sedimentary, but probably in part eruptive. 
Asphalt, petroleum, and coal, as well as salt, are also found in the county. 

LOS ANGELES. 


[Note.—D eterminations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

SILVERADO. 

Blue Light. 

Dunlap...,.-. 

Galena, pyrite, and quartz. 

Galena, zincblende, pyrite, (antimony and copper 
stains). 

Limestone and quartzite.... 
Quartzite. 

Probably diorite... 

Limestone and quartzite.... 
Shale. 

Probably diorite. 

Vein. 





MATtIPOSA COUNTY. 

This is the most southerly county on the gold belt, and contains many gold-quartz veins inclosed in slate. 
Argentite, proustite, and (it is said) silver telluride are also found. The southern end of the mother lode is in this 
county on the famous “Mariposa estate”. 

MABIPOSA. 

[Note.—D eterminations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

MARIPOSA. 

Hiti. . 

SEBA6TAPOL. 

Modesta. 

(Free gold, galena, copper pyrite, occasionally gold; 
pyrite, zincblende quartz, telluride ore.) 

Proustite, argentite, and quartz, (telluride ore). 

Graphitic slate. 

Graphitic slate. 

Vein. 

Probably vein. 
Vein. 

Coe. 

(Free gold quartz). 


(Slate)... 






NAPA COUNTY. 

In this as in the adjoining county, Lake, the principal useful mineral found is cinnabar, which occurs in the 
usual serpentinoid and arenaceous metamorphic strata. The Redington mine is one of the most important 
quicksilver producers in the state. 































































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


21 


NAPA. 


[Note. —Determinations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gaugue. 

• 

WALLS. 

Character of 

Foot. 

Hanging. 

deposit. 

OAT HILL. 

Napa Consolidated. 

Cinnabar, with sandstone and clay, (bituminous mat¬ 
ter). 

Cinnabar, metacinnabarite, marcasite, bitumen, 
quartz, (mispickel). 

Sandstone. 


Vein. 

Redington. 

Serpentine. 


Irregular bodies. 





MONO COUNTY. 

This county seems to contain two classes of deposits. The highly dor<$ silver, or low-grade gold of Bodie, is 
found in eruptive rocks of as yet undetermined character. A portion of the gold is free, but a large part of it is 
associated with complex silver sulphides, accompanied by quartz and calcite as gangue minerals. The other districts 
are granitic and carry chalcopyrite, copper glance, and carbonates, with galena, zincblende, argentite, and other 
silver minerals. 

MONO. 

[Note. —Determinations in parentheses are given on the authority of the experts.] 


Mine. 


BLIND SPRING. 
Comanche.. 


Diana and Kerrich. 


Modoc. 


BODIE. 

Bechtel Consolidated 
Bodie Consolidated .. 
Boston Consolidated. 
Bulwer. 


McClinton. 

Noonday. 

Oro. 

Standard Consolidated. 

Defiance. 

Goodshaw. 

Jupiter. 


HOMER. 


May bell_ 

May Lundy. 


INDIAN. 


Illinois. 
Tower.. 


Ore and gangue. 


Copper glance, chalcopyrite, zincblende, probably 
tetrahedrite, chrysocolla, (partzite, malacliito, clay, 
and quartz). 

Copper glance, cbrysocolla, copper carbonates, limo- 
nite (partzite and malachite), with earthy and (de¬ 
composed granitic gangue). 

Copper glance, chrysocolla, copper carbonates, (ga¬ 
lena and hom-silver). 


(Gold and silver bearing quartz). 

.do. 

(Gold and sHver bearing iron-stained quartz). 

(Quartzose and feldspathic vein matter carrying gold 
and silver.) 

(Gold and silver bearing quartz). 

..do... 

(Pyrargyrite and proustite). 

(Gold and silver bearing quartz). 

(Gold, silver, quartz, and feldspathic matter).. 

(Auiiferous quartz).. 

(Argentiferous gold quartz). 


WALLS. 


Foot. 


Granite. 


—do. 


(Porphyry) 


(Birdseye porphyry). 


(Porphyry). 

_do.. 

Indeterminable (volcanic). 

(Porphyry). 

(Volcanic). 


(Gold, silver, iron pyrite, galena, and quartz). 
..do. 


Tetrahedrite, zincblende, and quartz . 

Galena, zincblende, native silver, tetrahedrite, (pyrar¬ 
gyrite, pyrite, and quartz). 


Quartz-porphyry (?). 
Granite. 


(Granite and porphyry). 
_do. 


Hanging. 


Granite . 


.do. 


(Porphyry). 


(Birdseye porphyry). 


(Porphyry). 
—do. 


(Porphyry). 

(Volcanic).. 


Quartz-porphyry ? 
Granite. 


(Granite and porphyry). 
_do. 


Character of 
deposit. 


Vein. 


Do. 


Vein. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 


Vein. 

Do. 

Vein. 

Do. 


NEVADA COUNTY. 

Nevada has always been one of the most productive counties in the state, both the quartz and the placer 
mines yielding very large amounts. The quartz mines are for the most part in the slates characteristic of the main 
gold belt, but some of them are in granite, and some of them are on the contact between granite and slate. The 
gold is accompanied by iron and copper pyrites, mispickel, galena, and zincblende. As elsewhere in the gold belt, 
the proportion of silver is extremely small, even by weight. Though the larger part of the gold is free, the sulpliurets 
are ordinarily much richer than the quartz taken as a whole, and it usually pays to concentrate them and subject 
them to the Plattner chloridation process. The placer deposits are in part covered by volcanic rocks, chiefly basalt. 
The cap over a large area, however, is not so deep as to prevent the gravel from being worked, as it does to a 
considerable extent in the counties further north, while the amount of volcanic material has been sufficient to protect 
the gravel from extensive erosion. One of the great Tertiary rivers flowed through this county in a southwesterly 
direction and gave rise to the large gravel accumulations. 




























































































22 


PRECIOUS METALS. 


NEVADA. 


[Note.—D eterminations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

walls. 

Character of 

Foot. 

Hanging. 

deposit. 

9 

GRASS VALLET. 

Idaho. 

Free gold, galena, iron and copper pyrites, and some- 

Magnesian metamorphic 

Magnesian metamorphic 

Vein. 


times zincblende, quartz. 

Gold, pyrite, zincblende, galena, quartz, (copper 
pyrite). 

(Gold), pyrite, (zincblende, galena, iron, and copper 
pyrite), quartz. 

Pyrite and quartz. 

(Gold), pyrite, (galena, copper, and iron pyrite), 
quartz. 

(Gold, iron, and copper pyrite, galena, zincblende, and 
quartz.) 

rock. 

rock. 

Slate. 

Do. 



Metamorphic. 

Do. 

NEVADA CITY. 

Merrifield. 


Granite. 

Vein. 




Do. 






PLACER COUNTY. 

Placer lies directly across the gold belt, and is one of the principal producing counties. The gold-quartz veins 
occur for most part in slates, though some are found in granite, and they present the usual association of sulphurets. 
The auriferous gravels have been sufficiently protected by volcanic material to escape radical erosion without being 
so deeply covered as to be inaccessible. Iron-ore deposits are abundant. 


PLACER. 

[Note. —Determinations in parentheses are given on authority of the experts.] 


Mine. 

Ore and gangue. 

• 

WALLS. 

Character of 

Foot. 

Hanging. 

deposit. 

• COLFAX. 

Rising Sun. 

(Gold quartz). 


(Granite). 

Vein. 






PLUMAS COUNTY. 

The gold belt in the latitude of Plumas county is not so sharply defined as further south. Deposits of the 
precious metal, however, are abundant, both as veins and in gravel. The association of sulphurets accompanying 
the gold is the same as in Nevada county. The wall rocks are either slates and other metamorphic rocks or granite 
or both. The slates are sometimes so intersected by auriferous quartz as to give the veins a reticulated character. 
Although the production of the placer mines is considerable, a large part of the gravel is supposed to be inaccessible 
through the presenee of heavy overlying sheets of basalt. 

PLUMAS. 


[Note. —Determinations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 

Foot. 

Hanging. 

deposit. 

CHEROKEE. 





Plumas Eureka. 

(Gold), iron and copper pyrites, galena, quartz. 

Metamorphic diorite *. 

Metamorphic diorite *. 

Vein. 

GENESEE VALLEY. 





Genesee. 

(Gold), slate and quartz. 


Slatft 

Reticulated vein. 

Vein. 

Do. 

Do. 

Do. 

Vein. 

Placer. 

INDIAN VALLEY. 

Gold Stripe. 

(Gold generally free from sulphurets), quartz. 

(Slate). 


Green Mountain. 

(Gold, pyrite), quartz. 



Monitor. 

Gold, quartz... 



Plumas National. 

(Quartz), pyrite and mispickel. 

Slate. 


SENECA. 

Savercool.. 

(Gold), pyrite sandstone, and quartz. 

(Clay slate).. 


Sunnyside Gravel. 

(Auriferous gravels). 








* Examined microscopically 





























































































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


23 


SACRAMENTO COUNTY. 

The deposits of Sacramento county are mainly gravels, and are confined to its eastern and northern borders, 
where it adjoins Placer, El Dorado, and Amador. These gravels are in fact the western extremities of the extensive 
fields occurring in the more eastern counties. A larger product is usually accredited to the county than it 
actually yields, much bullion being shipped within its borders which is produced elsewhere. This is a consequence 
of the commercial importance of several towns of the county, among which is the capital of th'e state. 

SAN BERNARDINO COUNTY. 

There are veins in granite in this county which carry gold, copper, silver, and lead. There are also copper 
veins in limestone. Tin ore deposits are found at Temescal, where the ore is of an unusual character, but these 
are not now worked. Platinum sand is said to occur. 


SAN BERNARDINO. 

[Note. —Determinations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

CLARK. 

' 




Ally. 

(Argentiferous), stromeyerite. 

Limestone. 



Ivanpah. 

(Argentiferous), stromeyerite, copper earbonates, 

Limestone, probably dolo- 

Limestone, probably dolo- 

Do. 


(limestone). 

mitio. 

mitic. 


Lizzie Bullock. 

(Argentiferous), stromeyerite, copper carbonates, 

__do. 

do. 



(limestone). 



DBT LAKE. 





Desert Chief. 

(Silver ore), limonite, and quartz. 

(Granite). 

(Granite). 

Vein. 

Oriflamme. 

Free gold, limonite, and qnartz. 




SILVER MOUNTAIN. 






(Gold), stromeyerite, malachite, lead, and quartz... . _ 

(Granite).... 


Vein. 

BAN JACINTO. 





Cassiterite and quartz. 





Granitic or dioritio sand, said to carry platinum. 





SAN DIEGO COUNTY. 

There are some gold-quartz veins in San Diego occurring in metamorphic rocks and granite. Salt also forma 
one of the resources of this county. 

SAN DIEGO. 

[Note.—D eterminations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 

Foot. 

Hanging. 

deposit. 

BANKER. 

TTnhhard. 

Gold, sulphurets, and quartz. 

Slate. 

Slate. 


PINECATE. 

(Gold, copper and silver in traces), qnartz. 

(Granite and slate). 

(Granite and slate). 

Do. 

CAKGO MUCHACHO. 

Madre, Padre, and Cargo 
Muchaclio mines. 

(Free gold), qnartz. 

Metamorphic. 

Metamorphic. 

Do. 





SAN LUIS OBISPO COUNTY. 

There are several occurrences of cinnabar in metamorphic rocks, which appear to be similar to the more northern 
deposits of this ore. Chromic iron is found in considerable quantities. 

SAN LITIS OBISPO. 


Mine. 

Ore and gangue. 

WALLS. 

Character oi 
deposit. 

Foot. 

Hanging. 

BAN LUIS OBIBPO. 







Augitic porphyry. 

Augitic porphyry. 




Metamorphic *. 

Metamorphic.* 


BAN SIMEON. 






Sandstone. . 

(Shale). 

Impregnation. 

Polar Star. 

Cinnabar. 





Microscopically examined. 































































































24 


PRECIOUS METALS. 


SANTA BARBARA COUNTY. 

No important deposits, except of bitumens, are found in this county. 

SANTA BARB AHA. 

[Note.— Determinations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 

Foot. 

Hanging. 

deposit. 

SANTA BARBARA. 

Las Prietas. 

(Cinnabar, chrome iron). 


(Serpentine) - _ - 

Impregnation. 






SANTA CLARA COUNTY. 

The chief mineral resources of this county are the cinnabar deposits of the New Almaden and Guadalupe 
mines. They form irregular deposits, in many cases connected by veinlets of ore. The cinnabar is accompanied 
by pyrite, calcite, magnesite, and bitumen. Dolomitic limestone, shale, and serpentine are the inclosing rocks. 


SANTA CLARA. 


Mine. 

Ore and gangue. 

WALLS. 

• 

Character of 
deposit. 

Foot. 

Hanging. 

New Almaden. 

Guadalupe. 

Cinnabar, mercury, bitumen, calcite, magnesite, and 
pyrite. 

Cinnabar (and calc-spar),bitumen, magnesite, quartz . 

Limestone, shale, serpentine, 
and dolomite. 

Serpentine. 

Vein. 

Do. 


SHASTA COUNTY. 

There are veins in the schists and granites of this county which carry silver ores and gold associated with iron 
and copper pyrite, galena, and zincblende. A very remarkable occurrence is that of the Mad Ox mine, where 
native gold is found in calcite. The deposit is reported as a 2^-foot vein. The foot wall is schist and the hanging 
wall a siliceous limestone. Quartz and pyrite also occur in this vein as gangue minerals. Shasta contains some 
gold-placer mines. 

SHASTA. 

[Note.—D eterminations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

walls. 

Character of 

Foot. 

Hanging. 

deposit. 

IRON MOUNTAIN. 





Lost Confidence. 

(Silver and gold.) The silver is probably present as 
chloride, limonite, copper, pyrite, marcasite (argen- 
tite j the pyrite is rich), quartz. 

Suhiftt. 


Vein. 

NEAR IGO. 



Dry Creek, or Hardscrabble . 

(Gold). 

Slate bed-rock. 



PITTSBURGH. 




Placer. 

Potter Mining Co. 

Copper oxide, sulphide and carbonate, limonite, 
pyrite, (silver and zincblende). 

Slate (porphyry and slate).. 

Slate (porphyry and slate). 


SOUTH FORK. 


Chicago. 

Galena, pyrite, quartz, (chalcopyrite, antimony, ruby 
silver, native silver, gold, ana zincblende). 

(Granite)_ 



WHISKY CREEK. 



vein. 

Mad Ox. 

Native gold in calcite, limonite, quartz, pyrite, (sul- 
phurets and talcose schist). 


.. 




ibilic60ii3 lime 8 toil ft ...... 

Bo. 


SIERRA COUNTY. 


Sierra county lies between Nevada and Plumas, and shares the geological character of those 

its placer and quartz mines produce largely, but present no characteristics not shared by those 
regions. 


counties. Both 
of the adjoining 





































































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


25 


SISKIYOU COUNTY. 

Siskiyou county contains gold-quartz veins occurring in metamorphic rocks and accompanied by pyrite, 
mispickel, etc. Greenstone is reported as the hanging wall of the Black Bear and the Klamath, but no 
specimens of this rock have been received, and it is therefore impossible to pronounce with certainty as to its 
character. The principal product of the county, however, is derived from the placers, many of which are worked 
as drift mines. 

SISKIYOU. 

[Note.—D eterminations in parentheses are given on the authority of the experts. ] 


Mine. 


INDIAN CREEK. 
Bay City. 


Coyote Gulch.. 
Williams Drift 


M’ADAilS CREEK. 


Carroll Drift. 

Duncan Cameron. 

Hardscrabble. 

Hiyou Gulch. 

Lincoln, Hart, & Henry. 

Oak Grove. 

Siwash. 


OBO FINO. 

John Young. 

QUARTZ VALLEY. 

Johnson . 

8CIAD VALLET. 
Fort Goff Creek.. 


Thompson Creek.. 

YREKA. 

Pellet and Traitt_ 

SOUTH FORK SALMON. 

Black Bear. 

sawyer’s bar. 
Klamath. 


Ore and gangue. 


(Auriferous gravel). 


.do 

.do 


(Auriferous gravel). 

—do. 

— do. 

—do. 

_do .. 

_do. 

_do. 


(Auriferous gravel). 


Gold, limonite, and quartz. 


(Auriferous gravel). 
—do. 


(Auriferous gravel). 


(Gold, mispickel, and quartz). 


(Gold, pyrite, and quartz) 


WALLS. 


Foot. 


Argillaceous limestone bed¬ 
rock. 

Metamorphic bed-rock. 

.do. 


Slate bed-rock. 

.do. 

.do. 

Shale bed-rock. 

.do. 

.do. 

.do. 


Slate bed-rock. 


Brecciated metamorphio 
rock. 


Schist bed-rock. 
.do. 


Schist bed-rock. 


(Siliceous slate and quartz¬ 
ite). 


(Siliceous slate) 


Hanging. 


(Greenstone) 

(Greenstone) 


Character of 
deposit 


Placer. 

Do. 

Do. 


Placer. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 


Placer. 


Vein. 


Placer. 

Do. 


Do. 


Vein. 


Do. 


STANISLAUS COUNTY. 

This county lies to the southwest of Tuolumne and Calaveras. The mining interests are not large, and consist 
principally of placer deposits in its northeastern portion, near the boundaries of the counties just mentioned. The 
gravels of Stanislaus form an extension of those of the adjoining counties. 

SONOMA COUNTY. 

The only ores found are those of quicksilver, the chief mine being the Great Eastern. As usual, the ore is 
associated with pyrite and bitumen, the accompanying rocks beiDg sandstone, limestone, and a rock so highly 
metamorphosed as to resemble basalt until seen under the microscope. 

SONOMA. 


[Note. —Determinations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

GUERNEVILLE. 

Great Eastern . 

Cinnabar, bitumen, (pyrite). 

Sandstone and limestone ... 

Metamorphic *. 

Vein. 


Microscopically examined. 




















































































26 


PRECIOUS METALS. 


TRINITY COUNTY. 

Though gold-quartz veins occur, placers form the principal deposits of the county. The bed-rock in all the 
cases reported is sedimentary, and is usually slate. The Johnson mine shows beautiful occurrences of radial 
marcasite. 

TRINITY. 

[Note.—D eterminations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 
deposit 

Foot 

Hanging. 

CASON CHEEK. 


Schist bed-rock. 


Placer. 

Placer. 

Placer. 

Placer. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

DOUGLAS CITY. 


* 

Slate. 


INDIAN CREEK. 


Slate. 


RED HILL. 


Slate. 




Sedimentary. 




Slate. 












Slate. 






CINNABAR. 

AAeona. 

Cinnabar and quartz.- 

Serpentine. 



TUOLUMNE COUNTY. 

Tuolumne county lies across the main gold belt. Though placer deposits occur, the mineral wealth of this 
county is chiefly in the form of gold-quartz veins, which are found both in the slates and the granite. The minerals 
accompanying the gold appear to be independent of this difference in the character of the wall-rocks, and present 
the usual association of quartz with iron and copper pyrites, galena, etc. The mother lode runs entirely across this 
county. 

TUOLUMNE. 


[Note. —Determinations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 

Foot. 

Hanging. 

deposit. 

CONFIBBNCE. 

Confidence. 

(Gold, galena, pyrite, and quartz). 

(Granite). 


Vein. 

JAMESTOWN. 

Harris &. Healip. 

(Gold quartz). . 

(Slate) . 

(Slate). 


SONORA. 

Golden Gate. - . 

(Gold, galena, chalcopyrite, pyrite, calcite, and 
quartz.) 

(Gold, galena, pyrite, and quartz). 

(Slate). 

(Slate)... 

Vein. 

Vein. 

SOULBBYVILLE. 

Snnlahy_ 

( Granite^. 







VENTURA COUNTY. 

Bitumens yielding oil and sulphur deposits are found in Ventura 


YUBA COUNTY. 

Though there are quartz veins in this county, the principal deposits are placers, which, though they were among 
the first worked in the state, still yield largely. Comparatively little of the gravel is covered by lava. 

OTHER COUNTIES. 

Alpine, Colusa, Mendocino, Merced, Tehama, and Tulare counties all produce precious metals, though not in 
large quantities, and very little is known of the details of their occurrence, but there is nothing to lead to the 
supposition that the character of the deposits differs essentially from that of the quartz veins and placers of the 
better known regions adjoining them. 













































































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


27 


GEOLOGICAL SKETCH OF OREGON AND WASHINGTON TERRITORY. 

The topography @f Oregon and Washington territory bears a general resemblance to that of California. Near 
.the coast are low ranges, separating from the sea a long valley, to the east of which rise important chains. The 
mean rainfall in the western portions of this region is very great, and much country is covered by dense forests. 
To the east of the great ranges the climate and physical character of these two political divisions are similar to 
those of the adjoining territory of Idaho. Both Washington territory and Oregon produce coal in important 
quantities, but the precious-metal production of the more northern area is very small, while Oregon yields above a 
million a year in gold. 

Extremely little is known of the geology of these areas, which have been examined almost exclusively with 
reference to their bearing on doubtful points in the geology of regions to the south and southeast. Mr. King, in his 
Systematic Geology , gives the main facts known on the subject ; and some information regarding it is to be found 
in the Pacific railroad reports and in the American Journal of Science. 

As has been mentioned, the Sierra Nevada mountains were formed during a great post-Jurassic upheaval. The 
Cascade range, however, is more recent, although from a topographical point of view it might be regarded as a 
continuation of the great Sierra. The real northern representative of the Sierra is the Blue Mountain range of eastern 
Oregon, for both are due to the same orograpliical cause. The coast of the Pacific ocean of the Cretaceous period, 
therefore, bent eastward to the north of California, and followed the Blue Mountain range northward. The Blue 
mountains are composed, like the Sierra, of granite and metamorpliic strata, and in the latter Mr. King found 
Triassic fossils. It is probable that nearly or quite all of the metamorpliic rocks of Oregon east of the Blue range 
are Triassic or Jurassic. The Cascade range contains marine upper-Cretaceous beds, (a) but so far as is known none 
of later date, and it was probably raised above water-level at the close of the Cretaceous. It was certainly uplifted 
before the Miocene, for during this epoch a fresh water lake occupied the interval between it and the Blue mountains. 
West of the Cascade range, and near the coast on the other hand, Cretaceous and Tertiary strata predominate both 
in Washington territory and in Oregon, and it is probable that the coast ranges of Washington and Oregon, like 
those of California, were elevated chiefly by a post-Miocene disturbance. 

Throughout the Miocene immense volumes of lava reached the surface in Oregon and Washington territory, 
and the area occupied by it perhaps forms the largest lava field in the world. It spared an irregular belt along the 
coast and failed to cover the northeastern corner of Washington and part of eastern Oregon, but buried the rest of 
the country, in part to a great depth. 

Besides granite, the principal massive rock of Oregon and Washington is basalt, but andesites also occur in 
great quantities. The bed-rock of the Wickaiser mine, Ochoco district, Wasco county, Oregon, is sh*wn by a slide 
in the census collection to be diorite, proving at least that earlier eruptive rocks are not entirely absent. The ore 
deposits are chiefly veins in granite or metamorphic strata, and do not appear to be associated with volcanic rocks. 

Much the most important mining region of Oregon is Baker county, which lies in the southeastern corner of the 
state and adjoins Idaho. The gold veins of this region are in granite and metamorphic slates in and near the Blue 
mountains, and may thus be considered as occurring on a continuation of the gold belt of California. They are 
accompanied by auriferous gravels, which are of much local importance, though of greatly inferior volume to those 
of California and Idaho. The same arguments which are held to prove the Tertiary age of the gravels of California 
would probably apply to these also, but detailed information bearing upon the point is not available. Trias-Jura 
strata are also exposed in the Cascade range at a few points where the overlying material has been removed by 
erosion, and a little gold quartz and gravel have been discovered in such localities; for example, in Lewis county. 

In the northern part of California, as has been mentioned, the gold-bearing rocks have a wide distribution, and 
are not confined to a comparatively narrow belt, as they are in the middle of the state. Similarly the gold mines of 
Josephine and Jackson counties, which adjoin California and lie to the west of the Cascades, do not seem to bear 
a direct relation to the main rauges; but it is noteworthy that this region of scattered deposits in the two states is 
also that in which the Sierra and the Coast ranges meet, and are so entangled that as yet no one has succeeded in 
discriminating the two systems. The geological relations of the Skagit mines, in Washington territory, on the 
upper waters of the Skagit river, are not known further than that the gold is found in the bed of the present streams 
and that the surrounding country is mainly granitic. Auriferous sands are found on the southern coast of Oregon, 
as in northern California, and are worked as wind and tide permit. 

Coal-beds are frequent in the belt of country west of the Cascade range. Of these the most important are found 
at Coos bay, in Oregon, and at Bellingham bay, in Washington territory. The age of the Bellingham bay seams is 
known to be the same as that of the Monte Diablo coal or Upper Cretaceous, and those of Coos bay are probably 
also of this period. Iron ore is abundant, and has been smelted to a small extent, but under the disadvantage of 
high rates for labor. Quicksilver is found at the New Idrian cinnabar mine, Douglas county. Its occurrence seems 
to be similar to that of the California mines, and it represents the northern end of the series of deposits, the southern 
extremity of which is in San Luis Obispo county, California. It would be incorrect, however, to characterize this 
entire series as a “belt”, for toward the north the known occurrences are at long intervals. 


a These are of the Tejon group, and may prove to he Eocene. 




28 


PRECIOUS METALS. 


Whatcom and Yakima counties are the only ones in Washington territory from which gold mines are reported, 
though small quantities of gold are also obtained from the sands of the Columbia river, while King and Thurston 
counties produce coal. Oregon, Baker, Grant, Wasco, Douglas, Josephine, Jackson, and Umatilla counties are 
reported as containing gold mines. Coos yields auriferous beach sands and coal, Clackamas iron, and Douglas 
cinnabar. 

OREGON. 


BAKER COUNTY. 


[Note.—D eterminations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

BURNT RIVEE. 







Granite.. 

Granite. 

Vein. 

CONNER CREEK. 







Slate, basalt dike *. 

Slate, basalt dike *. 

Do. 

FARRIS GULCH. 







Granite..... 


Placer. 

POCAHONTAS. 






(Anrifernns gravel). 

Granite. 


Do. 


....do. 

Argillaceous sandstone. 


Do. 



Granite. 


Do. 


Quartz, gold, (and iron and copper pyrite). 

Slate. 

Slate. 

Vein. 

BYE VALLEY. 







Sandstone. 


Placer. 


Quartz stromeyerite, copper carbonates, (antimonide 

Granite ... 

Granite. 

Vein. 


of silver and iron pyrite). 




SHASTA. 







Gneiss. 


Placer. 

SILVER CREEK. 






Quartz, mispickel, pyrite, (stephanite, gold and silver 

(Unknown). 

Granite... 

Vein. 


bearing pyrite).*" 




WILLOW CREEK. 






(Auriferous gravel)... 

Slate . 


Placer. 


Quartz, gold, (iron and copper pyrite). 

Shale..... 

Shale . 

Vein. 







* Examined microscopically. 


Pioneer Black Sand 


COOS COUNTY. 


Magnetite, titanic iron, quartz, and gold. 


DOUGLAS COUNTY. 



Cinnabar, limonite, (feldspar, manganese oxide). 


Sandstone. 

Vein. 





GRANT COUNTY. 

ELK CREEK. 

Deep Creek. 

(Auriferous gravel)... 

Slate... 


Placer. 

Do. 

Vein. 

Placer. 

Do. 

Vein. 

Placer. 

Elk Creek. 

_do. 



GRANITE. 

Buffalo. 

Galena, pyrite, quartz, (stephanite and mispickel).... 
(Auriferous gravel). 

Quartzite. 

Slate.... 

Barne & Lucas. 

Shale. 


Klopp & Johnson. 

_do. 



Monumental. 

Tetrahedrite, polybasite, chalcopyrite, pyrite, quartz, 
(mispickel and zinchlende). 

(Auriferous gravel)... 

Granite. 


Trail creek. 

Granite.»_......._ 






JACKSON COUNTY. 

APPLEGATE. 

Chapel & Co. 

(Auriferous gravel). 

Slate.... 


Placer. 

Do. 

Placer. 

Placer. 

Grand Applegate. 

—do. 



UNIONTOWN. 

Gin Lin. 

(Auriferous gravel). 

Slate. 


STERLING. 

Sterling. 

(Auriferous gravel). 

Slate.... 






























































































































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


29 


JOSEPHINE COUNTY. 


Mine. 

Ore and gangue. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

GRAVE CREEK. 

Steam Beer. 

(Auriferous gravel). 

Slate... 


Placer. 

TANK. 

Sngar Pine. 

Galena, pyrite, chalcopyrite, and quartz. 




WASCO COUNTY. 


OCHOCO. 





Wlckaiser Si Co. 

(Auriferous gravel)..... 

Diorite *.... 


Placer. 






* Examined microscopically. 

WASHINGTON. 


YAKIMA. 


[Note.—D eterminations in parentheses are given on the authority of the expert.] 


TESHABTOX. 

Shaeffer... 


Metamorphic. 

Metamorpbie. 

Vein. 

SWANK. 

Swank. 

(Auriferous gravel). 

Sandstone (and slate) .*. 


Placer. 






GEOLOGICAL SKETCH OF NEVADA. 


That portion of the wide area included between the Sierra Nevada and the Wahsatch range, the drainage of 
which does not find its way to the sea, was called the Great Basin by Frdmont. The name has passed into general 
use, but with a somewhat extended signification, and, as commonly employed, includes to the south the desert 
region lying between the southern California ranges and the Colorado plateau, and to the north so much of Oregon 
as lies east of the Blue Mountain range and a somewhat indefinite portion of Idaho. The state of Nevada, with 
the western half of Utah, constitutes the larger and more important part of the Great Basin. 

Leaving the mountains out of consideration, the basin may be considered as a high plain with an average 
elevation of perhaps 4,500 feet; but the central portion is higher than the edges, the belt of country next west of 
the Wahsatch and that next east of the Sierra being about 4,000 feet above sea-level, while near the middle of 
Nevada the elevation is about 6,000 feet above tide-water. 

The Great Basin is strikingly characterized by rather short mountain ranges with nearly meridional trend, 
separated by valleys a few miles wide. The culminating peaks rise from 2,000 to 6,000 feet above the level of the 
surrounding country, and the ranges often present an imposing appearance, though they are greatly inferior to the 
Sierra and the Wahsatch as topographical features. Many of the valleys are totally devoid of vegetation, and 
present a surface of alkaline salts (mostly sodium chloride, carbonate, or sulphate), but the greater portion of the 
country is thinly clothed with “ sage brush”, low-growing shrubs with dull gray-green foliage, the most abundant 
of which is Artemisia tridentata; on the higher portion of the mountains, where a certain amount of moisture is 
supplied by the slow melting of the scanty snowfall, nut-pines, junipers, and mountain mahogany grow to a limited 
extent. The few streams are also fringed with narrow belts of vegetation. 

The principal rivers of Nevada are the Humboldt, the Carson, the Truckee, and the Quinn. All of these streams 
dwindle after reaching comparatively level ground by evaporation and absorption, and at last empty into small salt 
lakes which have no outlets. The alkali deserts unquestionably mark the positions of similar lakes now completely 
dried away. 

Though there are many contributions to the geology of Nevada, no complete survey of it has ever been made. 
The exploration of the fortieth parallel, however, covered a belt of 100 miles in width and extended across the 
state from east to west, beside taking in some outlying districts of importance; and most of the statements as to 
the general geology of Nevada in this account are derived from the publications of that survey. 

The Archoeau is exposed at a large number of points along the crests of the mountain ranges of Nevada, and 
these, taken in connection with the overlying strata, show that prior to the Palaeozoic era a mountain system covered 
the area of Nevada and extended to the east as far as the 104th meridian. This system, however, seems to have 
been entirely suboceanic, for the ranges were extremely lofty, yet they presented broader and smoother surfaces 
than subaerial erosion is ever known to produce. 

During the Palmozoic a continent occupied western Nevada and most of California, its eastern shore intersecting 
the 40th parallel in longitude 117° 30' (a few miles west of Austin) and trending nearly north and south. The 
sediments from this western continent, as well as from comparatively unimportant islands, accumulated throughout 







































30 


PRECIOUS METALS. 


the Paleozoic era on the sea-bottom, which subsided as the load increased, until the strata reached the enormous 
Miickness of 40,000 feet near the shore, thinning out to the eastward. The Palaeozoic was an era of extreme quiet, 
so that the geologists of the fortieth parallel were able to detect no unconformity in its strata. During the 
Carboniferous period the Palaeozoic sea was for the most part so deep that the sediments were almost exclusively 
limestones, in which it is hopeless to look for coal. Near the shore, however, land plants, associated with 
carbonaceous beds, occur in a single horizon, but even this is underlaid and overlaid by calcareous deposits and 
is of limited extent. At the close of the Palaeozoic era the land and the sea changed places. The sea-bottom, from 
longitude 117° 30' to and including the Wahsatch, rose above the surface of the water, while the continent which 
had stretched to the west sank and formed an ocean floor, upon which the sediments from the new continental area 
were deposited. The Triassic and Jurassic periods were also extremely quiet, and the strata are conformable 


throughout. 


At tlio close of tlio Jurassic age tlie western oceau, with its original floor of Archteau ranges overlaid by twenty odd thousand feet of 
conformable Trias-Jura sediments, suffered abrupt orographical uplift, resulting in the formation of a series of sharp folds and elevating 
a portion of the ocean area, extending from the eastern shore outward and west ward as far as the present west base of the Sierra Nevada, 
making an addition to the continent of 200 miles, the Sierra itself constituting the most western and most elevated of the newly-formed 
mountain ranges. The character of the orography of this period of disturbance is that of tangential compression, in which the gentler 
act ion was close to the old shore in the meridian of 117° and most powerful in the crumpled western slope of the Sierra Nevada, where the 
Triassic and Jurassic series have their enormous thickness crushed into a mass of almost indistinguishable folds, the rocks thrown into 
vertical dip and crowded together, making a belt of strata about fifty miles broad. This orographical action continued southward as far 
as the defined range of the Sierra Nevada extends and-northward along the whole shore of the Pacific, probably as far as the Alaskan 
peninsula. Passing northward from the region of the fortieth parallel, where the new addition to the continent measured about 200 
miles from east to west, the zone of crumpled Mesozoic was depressed so that the new ocean shore at the beginning of the Cretaceous age 
touched the west base of the Jurassic fold of the Blue mountains of eastern Oregon, (a) 


It is not certain that the whole system of Basin ranges dates from the post-Jurassic disturbance, for the 
corrugation of the Palteozoic area east of 117° might have accompanied its uplift immediately after the Carboniferous. 
There are considerable grounds, however, for supposing that uplift to have been comparatively quiet, and it is on 
the whole probable that all the ranges were raised by the same movement which crumpled the Trias-Jura strata of 
the Sierra. 

The views of the various geologists who have studied the basin ranges are not uniform as to the character of 
the dynamical action which resulted in the upheaval of these mountains. The geologists of the fortieth parallel 
regard the ranges as composed of synclinal and anticlinal folds more or less obscured by longitudinal compression 
and by faulting long subsequent to their upheaval. Pfaff (6) and others hold that faults are the extreme results of 
forces tending to form folds in an imperfectly elastic material, and that folds consequently frequently pass over into 
faults; and as long ago as 1870 Mr. Emmons (c) pointed out a case of this kind in the Toyabe range. Messrs. 
Powell and Gilbert, on the other hand, from investigations made mainly to the south ot the fortieth parallel belt, 
maintain that many of the uplifts are purely monoclinal in character. 

The Cretaceous is wholly wanting in the state of Nevada as well as in the great Sierra. This area was certainly 
above sea-level during that epoch, and if any fresh-water deposits formed they were swept away before Tertiary 
strata covered and protected them. Professor Whitney considers the absence of Cretaceous fossils in the Sierra as 
so remarkable that he infers the possibility that this area was unsuited to animal and vegetable life. ( d ) 

The Tertiary and the Quaternary eras in Nevada were characterized by the presence of lakes, which occupied 
different localities as orographical disturbances altered the drainage system. The present period of desiccation, 
during which evaporation has so increased and precipitation so diminished that the lakes no longer overflow and 
the salts brought into them by the streams are retained in nearly saturated solution, has not beeu a long one 
from a geological standpoint; and, according to Professor Whitney, it is shorter than that during which mau has 
been an inhabitant of the Pacific coast. Mr. King presents evidence to show that there has beeu more than one 
period of desiccation in the Quaternary. 

The massive rocks of the Great Basin are very numerous, and are referable to three distinct eras of eruptive 
activity. The granites are found only associated with Archman rocks, and never penetrate overlying strata. 
Important eruptions of diorite and diabase accompanied the post-Jurassic upheaval; while in the Tertiary and 
Quaternary andesites, rhyolites, and basalts were ejected in great quantities, usually reaching the surface along lines 
of disturbance established in the Mesozoic era. The crests of a large portion of the Nevada ranges are still covered 
by these lavas, among which rhyolite predominates. Propylite, which had been supposed to exist at a number of 
points in the Great Basin, does not appear to be an independent rock, but to represent a certain stage of 
decomposition, (e) 

Recent advances in the microscopical study of rocks tend to show that sanidin feldspar is of much rare 
occurrence than has hitherto been supposed. A recent revision (/) of the fortieth parallel collection by Messrs. 


a Exploration of the Fortieth Parallel, vol. i, p. 537. 
h Mechanismus der Gebirgsbilding. 
c Exploration of the Fortieth Parallel, vol. iii, 326. 


d Auriferous Gravels, p. 319. 

e Monographs United States Geological Survey, vol. iii. 

/ Third Annual Report of the United States Geological Survey. 





GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


31 


Hague and Iddings, to the results of which the writer has had access in advance of their publication, shows that 
there are probably no true trachytes among the rocks hitherto collected from the Great Basin. 

Ore deposits occur at a great number of points in Nevada, carrying gold, silver, lead, copper, and other useful 
minerals. They are not limited to rocks of any age. The Archman granite of Austin, the Palmozoic strata of Eureka 
and White Pine, and the Mesozoic rocks of Washoe are sufficient examples of this fact. The deposits occur in the 
mountains, as is usual the world over, and as the Nevada mountains are disposed in parallel ranges, of course the 
mines also occur in parallel belts. There is a perceptible tendency to the development of the same minerals at 
different points on the same belt, though there are no ore-bearing zones comparable in continuity with the gold and 
the quicksilver belts of California. The possibility that the deposits of Battle mountain, Austin, Caudalaria, etc., 
form a continuation of the Arizona belt has already been adverted to. 

In most cases it is impossible to determine the age of the deposits, yet there are many phenomena indicating a 
connection between them and eruptive activity, and they are probably for the most part referable either to the post- 
Jurassic period of upheaval or to that of the more recent volcanic eruptions. The gold veins of California, as has 
been explained, are post-Jurassic; and the Idaho gold veins are probably, at least in part, of the same age. It is 
difficult to suppose that the similar physical conditions prevailing in Nevada during the same period were not 
attended by similar mineralogical results. The Comstock, however, is probably very recent and a concomitant of 
volcanic eruptions in its immediate neighborhood. Mr. King drew attention (a) to the fact that no ore pebbles have 
been found in the Tertiary lake beds of Nevada, aud this statement still remains valid so far as the exploration of 
the fortieth parallel is concerned. Nor are prospectors known to have found any indications of ore in these beds. 
This negative evidence is all in favor of the supposition that the deposits are mainly Tertiary and post-Tertiary. 

The Comstock lode.— The Comstock lode is situated in Storey county, about 10 miles from the eastern limit 
of the Sierra, and lies on the east flank of the Virginia range. In twenty-one years it has produced a little over 
$306,000,000 worth of bullion, of which $132,000,000 was gold. The mines on this lode are the deepest in America, 
reaching a distance of over 3,000 feet from the surface, and containing 185 miles of galleries. The lode is extremely 
wide in places, and has been traced horizontally for about 4 miles. It dips east at an angle of about 45°. 

The Washoe district is almost entirely made up of eruptive rocks of post-Jurassic and Tertiary age. These 
are in large part highly decomposed, and both their character and the structural relations of the vein have given 
rise to much difference of opinion between observers. According to the latest investigation, (b) the most productive 
portion of the lode is associated with a hanging wall of diabase, while the foot wall in Virginia City is diorite, and 
in Gold Hill metamorphic slate. To the north and south of the most productive portion of the lode, which has 
hitherto been between the Union and Overman mines, the vein ramifies, only its northeastern branch remaining in 
contact with the diabase. 

A great fault attended the opening and filling of the vein. Its throw was nearly 3,000 feet at the middle of 
the lode, diminishing in each direction toward the extremities. The faulting action resulted in the formation of a 
system of fissures, which divides the country rock on each side into a series of parallel sheets. By this means the 
east wall, which was depressed by the fault, assumed near the surface the shape of a sharp wedge, and the 
projecting edge was broken through, giving rise to a secondary fissure, formiug an angle of 30° to 45° with the lode 
plane. The lode was charged with ore and quartz by lateral infiltration from the east or hanging side, these 
materials being deposited wherever there was an open space or a space filled with loose fragments to receive them. 
Of such spaces the secondary fissure, or “east vein”, as it has been called, afforded a large number, while below 
the junction of this fissure with the main lode such openings were comparatively infrequent. The fault mentioned 
did not take place all at once, and probably consisted of a great number of small movements, all in the same 
direction, extending over the whole period of ore deposition. Although small, these movements took place with 
irresistible force, and crushed such ore bodies as crossed the lines of motion to such an extent that their substance 
resembles ordinary commercial salt in texture and appearance. 

As is usually the case in silver veins, the distribution of ore in the quartz was by no means regular; a fact 
probably depending on the irregularity of the leaching process. While very little of the quartz is free from traces 
of precious metals, only certain spots contain enough to pay the expense of extraction, and are hence known as 
“ bonanzas”. ( c) These, however, commonly occur in the largest quartz masses. 

Though the Comstock is not just now in a flourishing condition, there seems to be no reason why large ore 
bodies should not yet be met with. The first condition for an ore body is a space to receive it. The existence of 
such openings depends upon mechanical conditions which are likely to be repeated at almost any depth, though 
a series of bonanzas on one level, such as was found in the “east vein”, is not likely to recur. 

It is highly probable that the depth to which the Comstock can be explored will be limited by the extraordinary 
heat. The Gold Hill mines have been flooded with water of a temperature of 170° F., aud as the temperature of 
the rock and the water increases on the whole in direct proportion to the depth boiling water may be met at 

a Exploration of the Fortieth Parallel, vol. iii, p. 7. 

I Monographs United States Geological Surrey, vol. iii. 

c A Spanish term, the nearest equivalent of which is “pay rock”. 



32 


PRECIOUS METALS. 


almost any time after the 4,000-foot level is reached. The heat of the water and the rock is a remnant of volcanic 
action. 

Austin.— The property of the Manhattan Mining and Milling Company is situated at Austin, Lander county, (a) 
It is famous for its steady yield of above $1,000,000 of silver a year from very rich but also very rebellious ores. 
The Toyabe range, on which Austin lies, is near the western edge of the Palaeozoic area which occupies the eastern 
half of the Great Basin. It has a granitic axis flanked by Palaeozoic strata, and is capped to a considerable extent 
by rhyolite. Other eruptive rocks occur in the range, which must be. for the present regarded as of uncertain 
character. The most important mineral deposits are found as veins in the granite, chiefly on the southern slope of 
Lander hill. 

Tlie outcrops on the hillside are very numerous, and many locations have been made; some within 10 or 20 feet of each other. Some 
of these outcrops have been proved by actual development to he well-defined and persistent fissures: others are probably mere seams or 
branches that pinch out or unite with stronger veins in depth; and that many must disappear in this manner seems apparent, from the 
fact that the number of veins or fissures cut in the deeper cross-cuts and shafts in various parts of the hill bear a very small proportion 
to the number of outcrops at the surface in their immediate vicinity, which, if persistent, would appear below. 

The developments on Lander hill show that within this mineral belt, running north and south, there prevails a zone more favored 
than the rest, within the limits of which the northwest and southeast veins traversing it are especially rich in ores of high value, and 
beyond which the proportion of base metals is greatly increased. This zone, so far as understood, also has a north and south direction. 
On Lander hill it may be from a quarter to a half mile in width. Its western limit is thought to pass through the Diana and the Savage 
mines, so that in passing from the southeastern to the northwestern portions of those claims a perceptible diminution of the richer and 
purer silver-bearing minerals, and an increasing predominance of baser metals, such as lead, copper, zinc, antimony, and iron, take place. 
Proceeding still further west, the proportion of rich silver minerals to the baser compounds becomes still lees, until the ore is quite too 
poor to pay for extraction. ( b ) 

The veins are comparatively very narrow, none, so far as reported, exceeding 3 feet. Many of them, however, 
are so rich that they can be worked with profit when showing only 3 inches of ore. The ore minerals are pyrargyrite, 
proustite, stephanite, polybasite, tetrahedrite, argentiferous galena, zincblende, and iron and copper pyrites. The 
amount of gold is said to be so small as not to pay for separation. The gangue minerals are chiefly quartz, 
manganese-spar, and calcite. Eear the surface the veins carried the silver as chloride, but at a depth of 150 feet 
this facile ore was replaced by the rebellious compounds above mentioned. There can be little doubt that the 
chloride was formed by the decomposition of the more complex minerals. 

The granite at a distance from the veins is extremely hard and tough, but near the ore it is much softer and 
shows signs of decomposition. A slide of this rock in the census collection shows that it is a normal biotite 
granite which has been subjected to the action commonly known as solfataric. The mica has been in part converted 
into chlorite, and in this latter mineral bunches of epidote crystals have developed, evidently at the expense of 
the chlorite, while the feldspar is scarcely affected. This fact, taken in connection with the relations of the altered 
rocks and the whole character of the occurrence, leads to the supposition that the veins were deposited by lateral 
secretion. All the veins are faulted to the north for a distance of about 200 feet, and Mr. Emmons considers it not 
improbable that this dislocation accompanied the eruption of the rhyolite which forms mount Prometheus. 

The age of formation of the veins is uncertain. The fact that faults have taken place since the ore was deposited 
is at least compatible with the supposition that the deposits are post-Jurassic; but were this the case, eruptive 
rocks of the same age would probably be formed in the neighborhood, while none such have been recognized. The 
formation of the veins is naturally connected with the metaphorism of the sedimentary rocks of the range, which 
seems to be due to later volcanic eruptions. The fact that the number of croppings occurring at the surface was 
larger than that of the veins found at a comparatively slight depth would also lead one to suppose that this 
multiplicity ot outcrops was a surface phenomenon, and that no great erosion had taken place since the ore was 
deposited. It is not impossible that the lines of fracture were established in post-Jurassic times, and that the filling 
of the veins and their dislocation occurred much later. 

The mines of the Manhattan Company cover a large extent of ground, more than a square mile, but the greatest 
depth reached is only 900 feet. The small size of the veins makes mining extremely expensive however, a very 
large amount of waste being necessarily extracted in stopiug the veins. The richness of the ore is indicated by the 
fact that it is mixed for roasting so as to give a tenor of $250. The milling process consists in crushing dry, 
roasting with salt in a Stetefeldt furnace, and amalgamation in pans. 

Eureka district. —The value of the ore deposits of Eureka was not determined until the year 1870, since 
which time, however, this has been one of the most important lead- and silver-producing districts of the country. 
It now produces about $4,000,000 of gold and silver, and nearly or quite 12,000 tons of lead annually. 

It is remarkable geologically as affording a very extensive section of Palaeozoic strata. It has recently formed 
the subject of a detailed investigation by Mr. Arnold Hague, whose monograph on the Geology of tile Eureka 
District will appear about the same time as this volume. He has kindly given permission to print the accompanying 
section, showing the average thickness and the succession of the rocks, and indicating by a double line a uon- 
eonformity in the Silurian, the first thus far discovered in the Palaeozoic of the Great Basin. 

a Mr. S. F. Emmons lias reported on tlie geology of the Toyabe range, and Mr. J. D. Hague on the mining and milling at Reese river. 
Exploration of the Fortieth Parallel, vol. iii. 

b Exploration of the Fortieth Parallel, vol. iii, p. 351. 








GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


33 


GEOLOGICAL SECTION OF THE EUREKA DISTRICT. 
By Mr. Arnold Hague. 



Upper coal measures . 

500 

Light-colored blue and drab limestones. 

$ 


O 

o 

CO 

Weber conglomerate . 

2, 000 

Coarse and fine conglomerates, with angular fragments of chert; layers of reddish-yellow sandstone. 

cT 


so 

p 

o 

Lower coal measures . 

3,800 

Heavy bedded dark-blue and gray limestone, with intercalated bands of chert; argillaceous beds near the 
base. 

«8 

*3 

o 


H 

Gj 

Diamond Peak quartzite ... 

3,000 

Massive gray and brown quartzite, with brown and green shales at the summit. 

& 


© 

White-pin© shale. 

2, 000 

Black argillaceous shales, more or less arenaceous, with intercalations of red and reddish-brown friable 
sandstone, changing rapidly with the locality. Plant impressions. 

o 

o 

© 


I 

§ 

> 

o 

a 

Nevada limestone ... 

6,000 

Lower horizons indistinctly bedded, saccharoidal texture, gray color, passing up into strata, distinctly bedded, 
brown, reddish-brown, and gray in color, frequently finely striped, producing a variegated appearance. 
The upper horizons are massive, well bedded, and bluish-black in color. Highly fossiliferous. 



X.onft Mnnnfjln limestone . 

1 800 

Black gritty beds at the base, passing into a light-gray siliceous rock, with all traces of bedding obliterated. 
Trenton fossils at the base. Halloysites in the upper portion. 

3 

© 


© 

Eureka quartzite .. 

500 

Compact, vitreous quartzite, white, bluish, passing into reddish tints near the base; indistinct bedding. 

i 

i 


Pogonip limestone . 

2,700 

Interstratified limestone argillites and arenaceous beds at the base, passing into purer, fine-grained limestone 
of a bluish-gray color, distinctly bedded. Highly fossiliferous. 

3 




350 

Yellow argillaceous shale layers of chert nodules throughout the bed, but more abundant near the top. 

, 


© 

«2 

Hamburg limestone . 

1,200 

Dark-gray and granular limestone. Surface weathering rough and ragged; only slight traces of bedding. 

o 

© 


1 

B 

•O 

a 

c3 

O 

S^-ret Canon shale (overlies the ore- 
bearing rock). 

1,600 

Yellow and gray argillaceous shales, passing into shaly limestone. Near the top interstratified layers of 
shale and thinly-bedded limestone. 

Prospect Mountainiimestone (incloses 
the ore deposits). 

3,050 

Gray compact limestone, lighter in color than the Hamburg limestone, traversed with thin seams of calcite. 
Bedding-planes very imperfect. 


Prospect Mountain quartzite (under¬ 
lies the ore-bearing rock). 

1,500 

Bedded brownish-white quartzites, weathering dark-brown ; ferrnginous near the base. Intercalated thin 
layers of arenaceous shales. Beds whiter near the summit. 


It appears from this table that the ore deposits lie in the lower horizons of the Cambrian. When they were 
formed is quite another question. The district shows a number of massive rocks, viz: Archaean granite and 
Tertiary or post-Tertiary andesites, dacite, rhyolite, and basalt. The eruptions most closely associated with the 
mines were rhyolite, and a connection between this rock and the ore may fairly be suspected; but the deposits are 
still under investigation, and something more satisfactory regarding their nature and genesis than any speculation 
which could be offered here will probably soon be ready for publication. 

The ores of Ruby Hill are argentiferous galena, accompanied by its decomposition products. Indeed, the larger 
part of the ore thus far mined is carbonate, mixed with some sulphate and ocher, as well as with mimetite and 
wulfeuite, the occurrence of which indicates the presence of considerable quantities of other metalliferous mineral 
besides galena prior to decomposition. The ore bodies are irregular, kidney-shaped masses distributed in limestone. 
This rock, though highly metamorphosed, is distinctly stratified in parts, and has been proved by Mr. Hague’s party 
to carry fossils which determine its age as Cambrian. The nature of these ore deposits has formed the subject of 
repeated lawsuits, and the many well-known geologists and mining engineers who have giveu testimony on the 
subject have expressed very discordant views, some holding them to be pipe veins in the limestone, while others 
regard the whole limestone formation between the quartzite and the shale as ore-bearing, the barren portions 
answering to the bone in coal seams. While the one party consider the small seams of ore sometimes found 
connecting the ore bodies as the rake vein corresponding to the pipes, the other party attributes these seams to 
the accidental presence of fissures, and ascribes no significance to them. The diversity of opinion developed as 
regards the deposits of Ruby Hill appears to indicate merely that large financial interests are involved in the title 
to this property, and not that there is anything exceptional in the character of the deposits themselves. Lead ores 
are more often found in limestone than elsewhere, and when so found almost always exhibit great irregularity in 
form and distribution. The fact is that little is definitely known with reference to the modus operandi of the 
deposition of galena. As Mr. Emmons, (a) in discussing the deposits of Leadville, has pointed out, if the hypothesis 


vol *13-3 


a Second Annual Report of Director of United States Geological Survey. 































































34 


PRECIOUS METALS. 


often advanced that this ore has been deposited in pre-existing caves were correct concentric structure would 
necessarily result. He regards it as more probable that the ore has been deposited by substitution for limestone. 
If this can be shown conclusively, lead deposits of this character would have to be regarded as veins differing 
from the usual type merely in the extreme irregularity of the walls; for an ordinary vein is merely an opening in 
the rocks, which is always limited in horizontal extent, and probably also in depth. Into such a fissure metalliferous 
solutions percolate and deposit ore minerals, precipitation being due to chemical or physical causes. Usually 
the walls of veins are chemically inert, and hence do not lose their original form ; but if the substance of the walls 
of a vein, instead of, e. (j ., infiltrations of organic matter, were to induce precipitation, that fact certainly would not 
deprive the resulting deposit of its character as a vein, though the shape of the walls might be strangely modified. 

A very remarkable feature of the Eureka deposits, shared to a greater or less degree by many others in the 
Great Basin, is the great depth to which decomposition, involving an accession of oxygen, has proceeded. The 
mines are between 1,200 and 1,300 feet deep; yet, although some water has been met of late, the permanent water- 
level has not been reached, and the amount of galena in the ore is scarcely more than enough to prove that the 
original lead mineral was the sulphide. The conversion of the galena to carbonate and sulphate, which must 
clearly be ascribed to the agency of atmospheric oxygen, could take place to such a depth only in an extremely dry 
country such as the Great Basin now is, and the decomposition must therefore have been accomplished since the 
early (Quaternary. 

CHURCHILL COUNTY. 

The product of this county has for the most part been confined to borax, but there are quartz veins in the IXL 
district occurring in granite and on the contact between granite and limestone. They carry silver and galena, but 
were not worked during the census year. 

ELKO COUNTY. 

The deposits of the Tuscarora district, in this county, are silver ores, including light and dark ruby silver, 
stephanite, argentite, and, near the surface, horn-silver. They are accompanied by pyrite. often argentiferous, and 
form veins in highly decomposed eruptive rock. This was formerly considered to be propylite, but from the slides 
and specimens of the census collection and of the fortieth parallel collection, and from known occurrences in the 
neighborhood, it is probable that the rock should be regarded as an altered hornblende andesite. 

ELKO. 

[Note.—D eterminations in parentheses are given on the authority of the experts.] 


Mine. 


Ore and gangue. 


•SUSCAROBA. 


Foot. 


Belle Isle. 

Argenta. 

Grand Prize 

Independence... 

Navajo. 

North Bello Isle 

Silver Star. 


Stephanite; gangue quartz, pyrite, and chalcopyrite.. Probably andesite* 

Horn-silver, dark and light ruby silver, and probably _do. 

stephanite; gangue country rock. 


Light and dark ruby silver, argentite, kora-silver near 
surface j gangue quartz, iron and copper pyrite, 
and zincblende. 


....do 


Horn-silver, (sulphides on lower levels), (quartz). 

Chloride; gangue, (quartz and spar). 

(Chloride, ruby, and argentiferous pyrite; gangue, 
spar, and quartz.) 


... do.. 

Andesite*. 

(Birdseye porphyry) 


(Antimonial ruby and argentiferous pyrite ; gangue, 
spar, and quartz.) 


(Porphyry) 



Character of 
deposit. 


Do. 


...do. 

Andesite *. 

(Birdseye porphyry) 


Do. 

Do. 

Do. 


(Porphyry) 


Do. 


* Microscopically examined. 


ESMERALDA COUNTY. 

Most of the mines of this county exploit deposits in the metamorphic slates and schists. These are broken 
through at numerous points by volcanic rocks, especially basalt, to which the solfatarie action attending the 
formation of the ores is possibly due. The ores resemble some of those found in Inyo county, California, carrying 
sulphautimonides of silver, argentiferous galena, tetrahedrite, copper and iron pyrite, zincblende, and pyrolusite, in 
a quartz gangue. There are also gold-quartz veins in granite, similar to those of California. In the Columbus 
district there is a nickel vein. 

The Northern Belle mine is sunk on a series of irregular deposits, forming a belt which is, in general, conformable 
to the. slates in which it lies. There is much basalt in the immediate neighborhood. Most of the ore is oxidized, 
but a few bunches of sulphurets are left, carrying galena, tetrahedrite, etc. The Northern Belle produces about a 
million a year. 







































GEOLOGICAL SKETCH OE THE PACIFIC DIVISION. 


35 


ESMERALDA. 

[IsOTE.—Determinations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

COLUMBUS. 





Mount Potosi. 

Gold and calcareous ocher, (lead, said to carry silver 

Slate. 


Vein. 


and gold); gangue quartz; (autimoniul compounds). 



Nickel. 

Nickel in an indeterminable form. 




Monte Diahlo. 

(Same as Northern Belle.) * 




Northern Belle. 

Horn-silver, malachite, galena, and tetrahedrite; 

Slate (called porphyry). 

Slate. 

Do. 


gangue, iron oxide, pyrolusite, pyrite, quartz, 




(zincblende). 




Victor. 

(Horn-silver, malachite, galena, and antimonial sil- 


(Slafp) . 

Do. 


ver); gangue quartz, and iron oxide. 



ESMERALDA. 





Real del Monte .. 

Gold, (copper); gangue quartz and iron oxide. 



Vein. 

OXEOTA. 




Tn titan Queen. 

Galena and chalcopyrite, (small quantities of sulph- 

Mica-schist. 


Vein. • 


antimonides of silver); gangue, pyrite, quartz, and 




zincblende. 




WILSON'. 





Wilson. 

(Gold); gangue quartz, iron and copper pyrites. 

Granite. 

Rhyolito and limestone. 


Wheeler. 

.do. 


. -. .do. 

Do. 






EUREKA COUNTY. 


The eliief deposits of this county, those of Ruby Dill, have been sufficiently enlarged upon. Most of the others 
are also of lead ores, and occur either in or close to limestone, but some of them, those for instance of Cortez district, 
are accompanied by copper minerals, native silver and mispickel, and some have more or less quartz as gangue. 
These are of especial value in smelting the prevailing extremely basic ores. 


EUREKA. 

[Note.—D eterminations in parentheses are given on the authority of the experts.] 


Ore and gangue. 

WALL8. 

Character of 
deposit. 

Foot. 

Hanging. 


(Limestone). 

(Limestone).. .. 

Irregular deposit. 

malachite’; gangue, zincblende, and mispickel, 



(quartz). 




Cerussite, (gold and silver, gangue qnartz and iron 

(Limestone). 

(Limestone). 


oxide.) 




(Carbonate, silver and gold, gangne quartz and iron 

Limestone. 

Limestone. 


oxide.) 




Argentiferous galena, cerussite, anglesite, mimetite, 

— do. 


Irregular bodies or 

wulfenite, with limonite and aragonite gangue. 



pipe veins. 

(Cerussite containing gold and silver, gangue qnartz, 

-do. 


Irregular mass. 

and iron oxide.) 




Cerussite, gangne quartz and iron pyrite. 


Shale. 


Argentiferous cerussite, gangue qhartz and iron 

Limestone. 

Limestone. 

Irregular mass. 

oxide. 




Galena and alteration products (telluride). 

Limestone. 

Limestone. 



Mine. 


CORTEZ. 


Garrison. 


EUREKA. 
Alexandria. 


Eldorado No. 2. 

Eureka Consolidated 

Jackson.. 

Richmond. 

Phoenix. 

Macon City. 


Silver Lick. 

secret caSos. 
Geddes &. Bertrand .. - 

EUREKA. 

Silver Conner. 


HUMBOLDT COUNTY. 

i 

Most of the veins are in the Mesozoic slates, and carry ruby silver and stephanite with iron and copper pyrite 
and mispickel in a quartz gangue. Near the croppings the silver takes the form of chloride. Some of the veins in 
the slates are worked for gold, but of these a part will probably be found to carry more silver than gold when the 
water-level is passed. The Pride of the Mountain, Winnemucca district, is reported to be on a contact between 

slate and granite. 






























































































36 


PRECIOUS METALS. 


HUMBOLDT. 


[Horn—Determinations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and ganguo. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

MOUNT ROSE, OR PARADI6E. 


Slate. 

Slate . 

Vein. 

Do. 

Do. 

Do. 

Vein. 

Contact vein. 


Chloride, pyargyrite, (ruby and stephanite); gangue 
quartz, p'yrite, mispickel, chalcopyrite, and iron 
oxide. 

_do. 



_do. 




....do. 


SIERRA, OR DUN GLEN. 
Lang Syne. 

Gold with quartz gangue. 

Silicified sedimentary rock 
(called porphyry). 

Silicified sedimentary rock 
(called porphyry). 

(Slate). 

WINNEMUCCA. 

Pride of the Mountain. 

(Sulpliurets and antimonial silver minerals, with 
quartz gangue.) 

(Slate) . 

(Granite). 


LANDER COUNTY. 

Besides the Austin mines, sufficiently described above, there are veins of ruby silver, etc., in quartzite, and of 
galena with quartz gangue in Palaeozoic slate. 

LANDER. 

[Note.— Determinations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

BATTLE MOUNTAIN. 






Galena, gangue pyrite and (quartz). . 

Slate. 

Slate. 

Vein. 

LEWIS. 




Starr & Grove. 

Ruby and sulphurets with (quartz gangue). 

Quartzite. 

Quartzite. 

Vein. 

REESE RIVER. 




Manhattan or Curtis. 

Dark and light ruby silver, stephanite, polybasite, 

Granite*____ 

Granite *. 

Vein. 


tetrahedrite, galena, iron and "copper pyrites, and 




quartz. 





* Microscopically examined. 


LINCOLN COUNTY. 

This county shows several classes of deposits. There is a considerable number of occurrences of galena and 
its decomposition products in limestone similar to those of Eureka and elsewhere, and which seem especially 
abundant in the Palaeozoic limestone of the Great Basin. The Meadow Valley and Raymond & Ely are also in 
metamorphic strata ; but these are quartzites, not limestones, and the character of the ore is correspondingly different. 
Below the water-level the ore consists of sulpliurets of unspecified composition; above the water-level it carries 
horn-silver, some gold, a little lead, and manganese. In the Eldorado district there are mines in a massive rock, 
probably diorite, which carry argentiferous copper minerals. 


LINCOLN. 

[Note.—D eterminations in parentheses are given on the authority of the expex-ts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 

Foot. 

Hanging. 

deposit. 

BRISTOL. 

Hillside. 

Galena and cerussile and (limestone). 


Limestone. 


Independence . 


Quartz-porpbyrvand shale.. 


Mendha. .. 

Galena and decomposition products. 

Limestone. 

Probably diorite. 


ELDORADO. 

January. 

(Horn-silver), iron oxide. 



Savage . 

Stromeyerite, quartz, and calcite. 


Vein. 

Pockets. 

JACK RABBIT. 

Dav ..* 

Argentiferous galena and lead carbonate, i-ed copper 

/ 

Limestone. 


ELY. 

ore and malachite, manganese oxide, (calc-spar and 
iron oxide). ’ 



Meadow Valley. 

(Gold, horn-silver, quartz, iron oxide, and manganese 

(Quartzite). 

(Quartzite). 

Vein. 


oxide.) 



Raymond & Ely. 

-do. 



Do. 

Brooklyn. 

Galena, zincblende, iron pyrites, (antimonial silver 
and quartz). 

Siliceous limestone. 

Siliceous limestone. 


* Microscopically examined. 




























































































































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


37 


NYE COUNTY. 

Argentiferous lead ores, inclosed in limestone in tlie usual irregular masses, veins of silver and copper ores, 
accompanied by slate or granite as well as limestone as wall rocks, and veins of arsenical and antimonial silver 
ores, inclosed in quartz-porphyry, are all found in Nye. The famous Belmont mine is on a vein in Silurian slate 
wliicli lies between granite and limestone. The vein is conformable with the slate, and carries sulpho-salts of copper, 
silver, and lead. 

NYE. 


[Note.—D eterminations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 

Foot. 

Hanging. 

deposit. 

BELMONT. 

Belmont. 

Galena, probably stephanite, quartz, pyrite, (snlphnr- 
ets of lead, copper, and silver). 

Sulphnrets, arsenical and antimonial silver minerals 
and mispickel. 

Enby silver and sulphnrets, arsenical and antimonial 
silver minerals, and manganese spar. 

_do....... 

Slate between granite and 
limestone. 

Quartz-porphyry*. 

Slate. 

Vein. 

MOKEY. 

'Bay State.. 

Quart z-porphyry *. 

Vein. 



__do .. 

Do. 



... do . 

Do. 

TTBO. 

Galena and decomposition products, (horn-silver, iron 
oxide, quartz, and argentite). 

Galena, horn-silver, (copper ores, native silver, lime¬ 
stone, and quartz), shale, zincblendc, and iron oxide. 


Limestone. 

Contact vein. 

UNION. 

Limestone. 

Limestone. 

Mineral belt 





* Microscopically examined. 


STOREY AND LYON COUNTIES. 

The only mines of importance in these counties are those of the Comstock lode, of which sufficient mention has 
been made. There are, however, other silver-bearing veins in eruptive rocks of this region, though none which have 
yielded large and steady profits. 

STOEEY AND LYON. 




WALLS. 


Mine. 

Ore and gangue. 



Character of 

Foot 

Hanging. 

deposit. 

THE COMSTOCK 







Diorite*. 

Diorite *. 

Vein. 





Do. 

Sierra N evada. 

Union Consolidated. 

Mexican. 

Opliir. 

California. 

Consolidated Virginia. 





Best & Belcher. 

Qnartz, argentite, native silver, and gold, occasionally 
stephanite, polybasite, etc., iron and copper pyrite, 
rarely calcite. 

^ Diorite *. 

Diabase *. 

Do. 

OOllltl cC UuIT) ............. 


















Exchequer. 

Alpha. 

Challenge. 

J 


1 


Confidence., 

Yellow Jacket. 

Kentuck. 

¥ 

Quartz, argentite, native silver, and gold, occasionally 
stephanite, polybasite, etc., iron and copper pyrite, 
rarely calcite. 

o) 

\ "Rlfw'lr filn.fi> * 


Do. 

Crown Point. 



Belcher., 


\ 

Quartz-porphyry,* diorite,* 
and metamorphics.* 

Diabase in part*. 

Do. 






do . 

...do. 

Diorite* and andesite*. 

Do. 


Eebellious silver ores in calcareous gangue . 

Quartz-porphyry * and meta- 
morpliics.* 

Dionte* and andesite*. 

Do. 





Microscopically examined. 


































































































38 


PRECIOUS METALS 


WHITE PINE COUNTY. 

The famous deposits of the White Pine district consist largely of horn-silver in irregular bodies in Devonian 
limestone. The chloride is accompanied by some lead minerals, however, and these predominate in the deposits of 
the base metal range near by. It is possible that the horn-silver of the Eberliardt & Aurora is a product of the 
decomposition of argentitc, and it is distinguished from ordinary occurrences in limestone by the presence of large 
quantities of quartz gangue, blit the admixture of lead minerals suggests that the ore bodies may be nearly related 
to the class of which the Eureka deposits are representative. There are also veins in the county associated with 
slate and massive rocks as well as limestone. These for the most part carry copper, besides silver and some gold. 
In the Robinson district theic are mines the ore of which is smelted for copper. They carry gold and silver in 
addition to the copper, and may represent extreme cases of the mineralogical association last mentioned. 

wttite pixe. 


[Note.—D eterminations in parenthesis are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 

Foot. 

Hanging. 

deposit. 

CIIERRY CREEK- 

(ITorn-silYer, argentite,) and quartz. 

Quartcite. 


Contact vein. 

Vein. 

Contact vein. 


(Pyrite, galena, stephanite, quartz, and calc-spar)_ 

Copper carbonates, sulpburets, (horn-silver, and quartz) 

Slate. 

Slate. 

Ticknp. 

Limestone. 





NEWAKK. 






Probably tetraliedrite, with carbonates. 

Limestone. 

Limestone. 


WAKD. 

Paymaster.. 

Probably stromeyerite and sulphantimonides, quartz, 
calc-spar, pyrite, zincblendo, and chalcopyrite. 

Slate, limestone, and prob¬ 
ably granite. 

Vein. 



WHITE PIXE. 





Eberliardt &. Aurora__ 

(Chloride, with siliceous limestone). 

Limestone. 


Impregnation. 

Do. 

Stafford.... 

_do. 








The remaining counties are of little importance at present. Washoe is one of the oldest mining counties, and 
contains base metal mines and silver veins, but its product is now very small, while the resources of Douglas, 
Ormsby, and Poop are undeveloped. 


GEOLOGICAL SKETCH OF UTAH. 

In northern Utah the Wahsatch range trends approximately north and south. It ends to the south about 
latitude 39° 30', but is nearly continuous with the western edge of the high plateau, which sweeps to the westward 
as the latitude diminishes. Together they form the eastern limit of the Great Basin, and divide Utah into two 
unequal parts, of which the western is the smaller. These two portions of the territory differ greatly. The Great 
Basin in Utah is characterized by the presence of the Great Salt lake and extensive areas of especially desolate 
alkaline desert, as well as by the system of mountain ranges mentioned in the description of Nevada. To the east 
of the basin lies an elevated area, of which the distinguishing characteristic is the horizontality of its strata. The 
general character of this region is that of a great undulating plain, though it is not utterly devoid of hills. Its? soft 
surface is deeply carved by modern streams into fantastic pinnacles and bluffs, which, added to the prevailing extreme 
barrenness, gives it a strange aspect, and a large portion of it has received the significant name of “bad lands”. 
This plain is broken in latitude 4(J° 30' by the great eastern and western ranges of the Uintah mountains, which are 
lot) miles long, and rises at its culminating point, Emmons peak, to an elevation of about 13,700 feet. It is unlike 
anj other range in America, being, in fact, a lolty forest-covered plateau, from which rise bare rocky peaks, 
composed, like the plateau, of nearly horizontal strata. It divides the Green River basin from the great plateau 
basin of the Colorado, but is cut through by the Green river. These two areas share the characteristics just 
described. 

The mineral resources of Utah are extensive and varied, and comprise lead, silver, gold, copper coal iron 
salt, sulphur, etc. ’ ’ 

All the government surveys have done moreor less work in Utah, but so far as the mining regions are concerned 
the chief sources of information are the publications of the exploration of the fortieth parallel and the geological 
volume of Captain Wheeler’s survey. Dr. J. S. Newberry has printed important papers on the subject, and Mr. G. 
K. Gilbert has published a jiaper on lake Bonneville, (a) 

The Wahsatch forms the boundary between two distinct geological regions. At the close of the Carboniferous 
the western poition of the Great Basin (including the area of the Wahsatch) was raised above the level of the 


a Second Annual Report Director United Slates Geological Survey. 











































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


39 


ocean, a position which it maintained throughout the Mesozoic era. The region to the east of the Wahsatch, on the 
other hand, remained undisturbed during the Trias and Jura, and underwent only gentle changes of elevation 
during the Cretaceous. The post-Jurassic upheaval, which folded up the Sierra Nevada and the Basin rauges, 
probably also had its effect upon the Wahsatch, but extended no farther. At the end of the Cretaceous a vast 
upheaval took place in the heart of the country, by which the whole system of the Rocky Mountain ranges was raised 
substantially to its present position, displacing the great gulf which had hitherto occupied this area. In this uplift 
the Wahsatch was involved, as is known, by the plication of the Cretaceous strata on its eastern slope; but the effect 
of the movement is not traceable further to the west. The Wahsatch range thus belongs geologically both to the 
system of the Basin ranges and to the Rocky Mountain system, and forms a broad boundary wall between the two. 

A great fault has taken place at the western side of the Wahsatch, which forms its foot wall. Had erosion not 
modified the range, it would be seen to consist of Mesozoic and earlier strata continuous with those of the country 
east of it but bent upward near the fault-plane, so that on the west of the crest there would be a gigantic cliff, 
cutting the strata nearly at right angles, while the eastern face would slope steeply away from the crest, but would 
gradually llatten and pass over into the nearly horizontal surface of the plateaus. To the south of the Wahsatch 
the plateau country was also elevated at the close of the Cretaceous, but its uplift was not attended or followed by 
any horizontal thrust sufficient to flex the strata near the line of upheaval into mountains. The Uintah range likewise 
dates from the post-Cretaceous uplift, and indicates a northern and southern compression, for its character is that of 
a broad anticlinal. Since the post-Cretaceous there have been further orographical changes, though none which have 
introduced new topographical features of importance. 

The great Wahsatch fault is a feature of the geology of Utah which has probably had an important influence 
on many of its geological phenomena, including that of mineral deposition. The geologists of the fortieth parallel 
have shown that, as far back as the Arclnean, a fault occurred along the range coinciding for the most part with its 
present western foot. Renewed dislocation on the same plane occurred at the close of the Cretaceous or early in 
the Eocene, again iu the Quaternary, and the fault appears to be in progress even at the present day, for so fresh 
is the most recently exposed surface that vegetation has not had time to clothe it. The observers draw the inference 
that such fractures in the earth’s crust always remain lines of weakness, liable on comparatively slight occasion 
to further dislocation. 

During the Trias-Jura the gulf or inland sea, of which the Wahsatch formed the western shore, was shallow in 
the northern and central portions of Utah, and the sediments consist of sandstones and shales, often cross-bedded 
by the action of currents. Numerous pools seem also to have been cut off from the main body of 1*he water, and thus 
to have been exposed to evaporation. The result is seen in frequent gypsum deposits, which are, for the most part, 
thickest at the center and thin out toward the edges. Such conditions are not favorable to marine life, and a very 
large part of the strata representing the Trias-Jura contain only fragments of vegetation from surrounding coasts. 
At the southern end of the territory during the Jurassic the sea was deep and deposited calcareous sediments. 

During the Cretaceous the water was for the most part shallow toward the north, and, in consequence of gentle 
oscillations in level, land and sea frequently alternated on the eastern side of the Wahsatch. Portious of the 
country, however, were maintained long enough above sea-level to permit of the growth of an extensive flora, and, 
as a consequence, the Cretaceous strata are marked by the presence of numerous carbonaceous beds, which often 
contain coal seams of fair thickness. In southern Utah the Cretaceous sea at certain points was deep, but 
throughout the plateau area most parts of it were shallow. 

After the post-Cretaceous uplift, and throughout the Tertiary, the region east of the Wahsatch was occupied by 
grfl&t fresh-water lakes, the sediments of which toward the north, and especially near the Uintah range, are deposited 
uncouformably ou the Cretaceous. In this region they are also unconformable among themselves, showing that 
orographical changes took place during their deposition. In southern Utah, however, the Tertiary freshwater 
strata appear to show no non-conformity either with one another or with the underlying Cretaceous. It is these 
fresh water Tertiaries which have been modeled by modern streams into the fantastic forms characteristic of the 
bad lands. Several large lakes existed in the Great Basin during this era, and similar conditions prevailed through 
the Quaternary, modified only in more recent times by slight orographical changes and by greatly increased 
evaporation. The great Quaternary lake of Utah was Bonneville, the history of which has been studied by Mr. 
G. K. Gilbert. According to that geologist the present dry period in the Great Basin is not the only one which it 
has experienced. A long remote period of drought, during which the lake sometimes nearly or quite dried up, was 
succeeded by a long wet period, in which, however, there was an insufficient supply of water to permit an overflow. 
Next oame a time so ».ry that the lake altogether disappeared, and then one of so much precipitation as to allow of 
discharge by overflow. This was followed by the present epoch, in which the arc® of water has been reduced to that 
of the Great Salt lake and the smaller bodies south of it. (a) 

The eruptive rocks of western Utah are the same as those of Nevada, and are represented by Arch jean granites, 
Mesozoic diorites, diabases, etc., and Tertiary or post-Tertiary andesites, rhyolites, and basalts. According to Mr. 
Hague, no true trachytes are found among the rocks collected in Utah by the exploration of the fortieth parallel. 


a Second Annual Report of the Director of the United States Geological Surrey. 







40 


PRECIOUS METALS. 


An interesting series of rocks, locally galled syenitic porphyries, has been collected in the West Mountain district, 
Oquirrh range, by the census expert, which seem to be highly augitic granite-porphyries. As in Nevada, there is 
an intimate relation between the ore deposits and occurrences of eruptive rocks, the former seldom being found 
except in the immediate neighborhood of the latter. 

Metallic ores are rare east of the Wahsatch and in the plateau country, where indeed Tertiary strata occupy 
much of the surface. In southern Utah, however, the Triassic sandstones carry silver and copper, and especially 
rich strata of this age form the famous silver reefs near Leeds. To the west of the Wahsatch and along the edge 
of the high plateau a series of ore deposits is found from one end ®f the territory to the other, forming a true 
mineral belt. All of these are associated with Palaeozoic strata, which, however, proves nothing as to the age of 
the deposits; indeed, it is known that some of them must be Tertiary or post-Tertiary. It seems extremely probable 
that these ore deposits owe their existence to the solfataric action accompanying the eruption of massive rocks, and 
that the points where these reached the surface were determined by the line of disturbance, of which the great 
Wahsatch fault is the most striking manifestation. At all events, it is a fact that the western edge of the post- 
Cretaceous uplift is marked in Utah by an immense number of deposits. It has been pointed out on a preceding 
page that there is a strong analogy between the geological relations of the mineral belt of Utah and those of 
California. There are ores in the Basin ranges of Utah as well as near the Wahsatch, and particularly in the 
Oquirrh mountains, which lie to the west of Utah lake. These are very similar to the deposits in the kindred ranges 
of Nevada. 

The prevailing type of the ore deposits in Utah consists of more or less regular bodies of argentiferous lead 
ores associated with limestone, and usually accompanied by eruptive rocks. The original form of the ore was 
probably in all such cases galena, which in a majority of instances has yielded to decomposition processes for a long 
distance from the surface, and is now replaced by carbonate, sulphate, and other secondary minerals. Of such 
occurrences the Horn Silver mine is an excellent type and an important instance. The deposit worked by this 
mine lies between a foot wall of dolomitic limestone and a hanging wall of rhyolite. The nature of this lava is 
proved by microscopic slides in the census collection. Small masses of galena occur, but the prevalent mineral is 
the sulphate which has formed in consequence of oxidation of the galena. It is a significant fact that heavy spar 
is one of the gangue minerals, but occurs only near the rhyolite. The same district shows other volcanic rocks. An 
augite-andesite is found near the Horn Silver mine, and the Carbonate miue, near by, is associated with a hornblende- 
andesite of‘so-called “ trachytic” habitus similar to the Mount Bose hornblende-andesite of the Washoe district. 

The veins in Utah which are associated with slates or quartzites do not commonly carry a preponderance of 
lead ores, but are cupriferous and sometimes auriferous$ the gangue in such cases is also generally quartz. Of such 
mines the Ontario is much the most important. 

The Ontario mine in the Uintah district, Summit county, is a strong vein, several feet wide. Its ores are 
zincblende, galena, fahlerz, and pyrite, with some horn-silver and copper carbonate in a quartz gangue. The walls 
are, in the main, quartzite, but at 400 feet a porphyry was struck near the vein which appears at lower levels in 
contact with the vein, and it is thought will replace quartzite as the hanging wall. Unfortunately the specimens 
of this porphyry received are too much decomposed to make determination possible. It is full of pyrite, and has 
manifestly been subjected to solfataric action. The Ontario is one of the richest mines in the country. Its ore is 
treated by roasting in a Stetefeldt furnace and amalgamation. 

The sandstones of southern Utah and the adjoining regions carry a very unusual form of ore deposits, 
consisting of impregnations of silver and copper, partly native and partly as sulphides. Much of the silver sulphide 
has also been converted into chloride. The age of these sandstones was determined by Professor J. Marcou, and 
subsequently by Dr. J. S. Newberry, as Triassic—a determination confirmed by Messrs. Gilbert and Howell. ( a) 
The geological information which has been published on this subject is very largely due to Dr. J. S. Newberry, (b) 
After having described the peculiar character of the Triassic sea in this portion of the continent and mentioned the 
well-known facts regarding the silver contents of ordinary sea-water, this geologist states his opinion as to the origin 
* of the silver and copper in the sandstones as follows : 

In ear the Utah shore oi this Priassic basin the water would seeui to bave been more highly charged than elsewhere with silver 
thongh it was also the associate of the more abundant copper in New Mexico, the Indian territory, and Texas. Doubtless this silver 
was brought up in springs on the old land from the same sources which furnished so large an amount of silver to the fissure veins formed 
there long after. Near the old shore the drift-wood brought down by the draining streams and scattered by the shore-waves, when 
buried in the accumulating sediment, became more or less replaced by copper and silver, precipitated by the reducing action of organic 
matter which is manifested in so many different ways. The quantity of silver in some of the bays and estuaries carried by draining 
streams, perhaps fed in part by mineral springs, may have been greater than that in most parts of the water-basin, and hence the 
sediments formed there hold a quantity larger than the average. We find the same variation in the distribution of copper farther east. 
In some places it was so abundant that it was not all taken up by the decaying wood, but formed concretions of sulphide in the sand or 
clay. 

***»**,, 

The ores of silver and copper plainly existed as solutions, which saturated the sand when it was collected and deposited the 
sulphides with sandstone after the mechanical action which transported the sediment was at an end. All this, however, was within the 
Triassic age, while the water was shallow and highly charged with mineral matters. 


a Surveys West of the 100 th Meridian, vol. 2, p. 176. 


b See especially Engineering and Mining Journal, vol. 31, p. 5. 





GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


41 


He states later in the same article that he regards it as possible, th»ugh not probable, that in some places the 
porous sandstones of the Trias were penetrated by solutions, from which the sulphides of copper and silver were 
precipitated. 

The undisturbed condition of some of the sandstones is certainly an argument in favor of the supposition that 
the ore was deposited with the sandstone, but there are considerable difficulties involved in its acceptance. 
Common sea-water will dissolve only an extremely small amount of silver salts, though saturated solutions of salt 
are capable of dissolving silver chloride in considerable quantities. If the Triassic sea held the silver in solution, 
it can only have been charged with the metal after isolation from the main ocean and concentration by evaporation; 
but it is difficult to suppose this combination of conditions prevailing over wide areas. The deposits of commern 
in Rhenish Prussia present very strong analogies to those of Silver Reef, but there it is an argentiferous, though 
otherwise very pure galena, which is disseminated through sandstone. There are strong chemical objections to 
supposing this galena to have been deposited directly from the ocean, or even from a land-locked basin of 
concentrated sea-water; yet a satisfactory theory would give an account of it as well as of the Utah silver. The 
theory of impregnation of the sandstones by solution presents, in my opinion, fewer difficulties. It is not easy to 
see why the replacement of organic matter, such as wood, by the metals would not occur as readily from an 
ascending solution as from sea-water, while ascending solutions would certainly favor the formation of the 
considerable nodules of ore sometimes found in the sandstone. May these deposits not, after all, be chemically 
and physically analogous to ordinary veins, though so different from them structurally"? It is supposed that 
precipitation takes place in veins where there is room for deposition, and where at the same time relief of 
temperature and pressure or chemical action, especially that of organic matter, induce precipitation. In ordinary 
rocks such conditions are to bo fouud mainly in fissures, but in sandstones, particularly such as carry organic 
matter, they may occur anywhere, and the presence of copper or lead would be as readily accounted for as that of 
silver. Dr. Newberry records that analyses made at his instance by Mr. J. B. Mackintosh show that the silver 
in some of the sandstones is accompanied by selenium in considerable quantities. 

The number of workable coal-seams in Utah is very considerable. Those thus far opened lie for the most part 
on the eastern flank of the Wahsatch, or not far from the western edge of the high plateau, and while search for 
them elsewhere is by no means hopeless, these localities seem most likely to show good seams. Both Cretaceous 
and Tertiary beds are said to occur, (a) and some of them are reported to present very unusual qualities for coals of 
such recent date, not crumbling on exposure, containing a very small amount of water, and yielding strong coke. 
The great value of such beds, at an immense distance from the well-explored coal-fields of the Carboniferous^era, 
is patent. 

In the appendix will be found a report on the mining industries of Utah by Mr. D. B. Huntley, who filled the 
office of special expert for the territory. This paper describes the mineral resources in so much detail that any 
special notes on the counties are unnecessary here. 

BEAVER. 

RTote.— Determinations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 

Foot. 

Hanging. 

deposit. 

BRADSHAW. 






Cerussite, cuprite, copper carbonates, with calcite, 
aragonite, and limonite, (manganese oxide, native 
sulphur). 

Cerussite and anglesite predominate; galena, dufre- 
noysito, proustite, (pyrargyrite), eerargyrite, argen-. 
tite also occur with calcite, quartz, and barite. 

Argentite, argentiferous galena, cerussite, and quartz. 

Galena, cerussite, and calcite, (iron oxides and quartz). 

Copper carbonates, calcite, (iron oxides, said to carry 
lluorspar). 



Irregular bodies. 

Chimney. 

Vein. 

8AN FRANCISCO. 

Limestone. 

Rhyolite *. 


Hornblende-andesite *. 

Hornblende-andesite *. 


Limestone. 

Limestone.. 

Irregular bodies. 
Pipes. 


Limestone and slate. 

Limestone and slate. 




6T.VR. 







Black limestone. 

Black limestone. 



Cerussite, horn-silver, malachite, and quartz. 

Limestone. 

Limestone. 



Galena, cerussite, gypsum, and pyrolusite, (limonite).. 

Dolomitic limestone. 

Dolomitic limestone. 

Chimney. 


• 

Siliceous limestone. 

Siliceous limestone. 


Galena, (cerussite and iron oxides). 

Limestone_ . . 

Limestone. 


Vicksburg. 

Galena, cerussite, free sulphur, gypsum, and quartz, 
(limonite). 

TTemntite and limonite used as flux. 

Crystalline limestone. 

Granite *. 

Crystalline limestone. 

Limestone. 



Galena, cerussite, and clay, (limonite, little gold, or 
silver). 

Dolomitic limestone. 

Dolomitic limestone. 

Chimney. 





* Microscopically examined. 


a E. E. Howell in Surveys West of the 100 th Meridian, vol. 3, p. 278. 






























































42 


PRECIOUS METALS 


JUAB 

[Note. —Determinations in parentheses are given on the authority of the experts.] 


Mine. 


TINTIC. 


Bonanza. 
British . - 


Carisa. 

Elmer Bay.. 
Eureka Hill. 


Ore and gangue. 


Golden Bell. 

Golden Treasure. 


Joe Bowers 
Mammoth .. 


Mammoth Copperopolis. 

Morning Glory. 

Park...-. 


Rising Sun 
Shower .... 
Swansea... 


(Galena, pyrite, and other minerals).. 

(Copper minerals, limonite, calcite, quartz, rarely 
gold, and manganese oxide.) 

Quartzose, carrying limonite and lead, probably as 
cerussite, (copper carbonates and sulphides). 

Eruhescite, anglesite, pyrite, mispiokel, quartz, (lim¬ 
onite). 

Galena and its decomposition products, copper stains, 
hematite, quartz, calcite, (lead ocher, gold, hom-sil- 
ver, and zincblende). 

Bismuthite (argentiferous). 

Siliceous and ferruginous rock (carries bismuth and 
silver). 

Ferruginous quartz, ealcite, and cerussite (?). 


WALLS. 


Foot 


(Porphyry) . 
(Limestone) 


Probably dacite, * (lime¬ 
stone). 

Hornblende-andesite*. 


Siliceous limestone 


Cuprite, pyromorphite, copper carbonates, quartz, cal¬ 
cite, pyrolusite, (limonite, argentite, and horn-sil¬ 
ver). 

Enargite, malachite, quartz, pyrolusite, (silver). 

Anglesite, iron oxide, and quartz. 

Galena, cerussite, quartz, (limonite and silver, prob¬ 
ably as argentite). 

Argentiferous pyrolusite, (galena, gold, and copper)... 

Galena, cerussite, calcite, and quartz. 

(Galena, cerussite, limonite, and quartz).. 


Indeterminably decomposed 
massive rock. 

Andesite, (?) decomposed 
anil pyrititerous. 

Dolomitic limestone. 


Hanging. 


(Porphyry). 
(Limestone) . 


Probably dacite, * (lime¬ 
stone). 

Hornblende-andesite *. 

Siliceous limestone. 


Character of 
deposit. 


Pipes. 

Mineral belt/ 
Vein. 

Do. 

Irregular masses. 


Limestone . 


Diorite*. 

Hornblende-andesite * 

(Granite) (?). 


Indeterminably decomposed j Vein, 
massive rock. 

Andesite, (?) decomposed 
and pyritiferous. 

Dolomitic limestone. 


Lime^one. 


Diorite *. 

Hornblende-andesite * 

(Granite) (?). 


Vein. 

Vein. 

D* 

Do. 


* Microscopically examined. 

PIUTE. 

[Note.—D eterminations in parentheses are given on the authority of the experts.] 


OHIO. 


Bully Boy... 
Copj*r Belt. 


MOUNT BALDT. 

Deer Trail. 


Green-Eyed Monster 

Pluto . 

Lucky Boy. 


Galena, quartz, (cerussite). 

Melaconite, (?) copper carbonates, iron oxide, (tetra- 
hedrite, chalcopyrite, chalcosite, and quartz). 

Galena and decomposition products, malachite, wul- 
fenite, quartz, (lead ocher and copper sulphides). 

__ do. ... 

Argentite, free gold, and calcite. 

Quicksilver selenide. 


Ouartz-Dorphvrv *. 

Quartz-porphyry*. 

Quartzite.-. 

Limestone. 


.... do . 




Vein. 

Contact vein. 
Do. 


* Microscopically examined. 

SALT LAKE. 

[Note. —Determinations in parentheses are given on the authority of the experts.] 


BIG COTTONWOOD. 


Anellie. 

Antelope & Prince of Wales. 

Butte.*.. 

Carbonate. 

Maxfieid. 


Ophir. 


Reed &. Benson . 
Silver Mountain 


Thor & Bright Point. 

little cottonwood. 

Cincinnati.. 

City Bocks.. 


Melaconite andmalnchite, (lead, silver, and gold)_ 

Galena, limonite, copper stains, and calcite, (cerussite 
and manganese oxide). 

Galena, limonite, calcite, pyrolusite, and quartz. 

Galena, cerussite, limonite, and calcite. . 

Galena, cerussite, malachite, pyrite, quartz, calcite, 
talc, (manganese oxide and limonite). 

Galena, cerussite, copper stains, pyrolusite, and iron 
oxide. 

Cerussite, plumbic ocher, anglesite, and calcite. 

Galena, cerussite, plumbic ocher, (copper stains, 
quartz, and limonite). 

(Galena, cerussite, limonite, and quartz).. 


(Limestone).' (Limestone). 

| Limestone.j Limestone. 

-do. —do. 

Dolomitic limestone. Dolomitic limestone. 

Limestone. Limestone. 


Dexter . 
Emma . 


Emily 


Equitable.. 
Evergreen . 
Grizzly 


Louise. 

North Star. 


(Galena), cerussite, anglesite, and pyrolusite. 

(Galena), cerussite, wulfenite, cuprite, malachite, py¬ 
rolusite, and limonite. 

Galena anti quartz. 

Galena, cerussite, anglesite, limonite, calcareous 
gangue, (manganese minerals). 

Galena, dufrenoysite, pyrite, calcareous gangue, (tet- 
rahedrite, zincblende, and quartz). 

(Galena and cerussite). 

(Galena, cerussite, limonite, and copper carbonates).. 

Cerussite, copper stains, limonite, and manganese 
minerals. 

(Limonite, quartz, with galena and cerussite). 

Galena, cerussite, and wulfenite. 




Blue limestone. i Blue limestone. 


Limestone. 

Quartzite and shale. 

Quartzite. 


Limestone and diorite * 


Limestone. 

Quartzite and shale. 


Quartzite. 


Limestone and diorite. 


Limestone. Limestone 


(Quartzite) 


Vein. 

Bedded vein. 


Bedded vein. 
Vein. 


Belt. 


(Limestone). 

(Limestone and sandstone). 
Limestone. 


(Limestone) 
Limestone .. 


(Quartzite) .j Vein. 

(Limestone). 

(Limestone and sandstone). | 
Limestone. 


(Limestone) 
Limestone .. 


Vein. 

Vein or belt. 


















































































































































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


43 


SALT LAKE—Continued. 


Mine. 


UTTLE COTTONWOOD—COnt’d. 
Oxford & Geneva. 

Toledo.~. 

Vallejo. 

Victoria & Surpriser. 

W ellington. 

WEST MOUNTAIN. 

Highland Boy. 

Jordan . 

Live Yankee. 

Lucky Boy . 

May Flower. 

Neptune. 

Old Telegraph. 

Queen. 

Stewart. 

Stewart No. 2. 

Telegraph lit W. Extn. 

The Lead Mine. 

Tiewankee. 

Victor. 

Winnamnck. 

Yosemite... 


Ore and gangue. 


Galena, cernssite, plumbic ocher, wad, ennrgite, py- 
rite, chalcopyrite, malachite, marcasite, calcareous 
gangue, (oxide of manganese and quartz). 

(Hematite, quartz carrying silver).. 


Galena, cernssite, anglesite, copper stains, limonite, 
hausmannite, and wulfenite. 

Cernssito, limonite, probably horn-silver. 

Galena, zinchlende, copper pyrite, (limonite, silver, 
and gold). 


Galena, chalcopyrite, (gold). 

Galena, (gold), iron and copper pyrites, cernssite, limo¬ 
nite, quartz, and copper stains. 

Galena, cerussite, limonite, and quartz. 

Orpiment and realgar. 

Gold, quartz, and limonite.. 


Zinchlende, galena, pyrite, (silver and gold).. .. 

Galena, oerussito, iron and copper pyrites, malachite, 
limonite, and quartz. 

Galena, cerussite, argentite, pyrargyrito, rhodocrosite, 
zinchlende, quartz, barite, (bornito, calcite). 

Gold, quartz, limonite, galena, and chalcopyrite. 

Gold, quartz, limonite, (silver and copper carbonate).. 

Cerussite, quartz, (galena and limonite). 

Cerussite and quartz. 

Galena, binnite, zinchlende, pyrite, cerussite, quartz, 
iron oxides, (ruby silver and native silver). 

Cerussite, (silver and gold).. 

Galena, dufrenoysite, iron and copper pyrites, cerus¬ 
site, limonite, zinc-vitriol efflorescence, native sul¬ 
phur, (zinchlende, cubanite, tetrahedrite, calcite, 
and gypsum). 

Galena, cerussite, iron and copper pyrites, melaconite, 
limonite, (bornite, zinchlende, anil quartz). 


WALLS. 


Foot. 


(Quartzite), 
Dolomite... 


(Black limestone). 


Quartzite. 
_do. 


Granite-porphyry* 


(Between granite and quartz¬ 
ite.) 

Limestone. 

_do.. 


Angitic granite 
phyry. (?)* 

Quartzite. 

(Unknown). 

(Quartzite). 

Quartzite. 

...do . 


por- 


(Qnartzite) 
Quartzite .. 


...do 


Hanging. 


(Quartzite) 

Dolomite. 


(Black limestone). 


Limestone. 
Siliceous limestone 

Granite-porphyry. * 


(Between granite and quartz- 
ite.) 

(Quartzite). 

Quartzite. 


Character of 
deposit. 


Angitic granite 
phyry. (?)* 

Quartzite. 

_do.. 


por- 


(Quartzite) 
Quartzite. . 
— do. 


(Quartzite) 
Shale. 


Quartzite 


Vein. 


Vein. 


Vein. 


Vein. 

Belt. 

Vein. 

Bedded vein. (?) 
Vein. 

Bedded vein. 
Belt. ' 

Do. 

Vein. 

Bedded vein. 

Vein. 


* Microscopically examined. 

SUMMIT. 

[Note. —Determinations in parentheses are given on the authority of th.e experts.] 


UINTAH. 
Empire. 

Fairview. 

Ontario. 

White Pine. 

Walker & Webster 
Boss. 

Woodside. 


(Horn-silver), malachite, (cerussite), quartz, manga¬ 
nese oxide, and limonite. 

Cerussite, plattnerite (?) with calcareous gangue. 

Galena, argentite, (native silver), tetrahedrite, zinc- 
blende, (pyrite), horn-silver, malachite, clay,(quartz). 

Galena, zinchlende, pyrite, cerussite, malachite, (tet¬ 
rahedrite, argentite, and native silver). 

Galena, cerussite, and quartz. 

(Zinchlende, galena, cerussite, horn-silver, copper car¬ 
bonate, manganese oxide, limonite, and quartz.) 

(Cerussite, anglesite, galena, iron oxide, and calcite)... 


Quartzite. 

(Quartzite). 

Quartzite. 

Limestone. 

« 

(Siliceous limestone) 
(Quartzite). 


(Said to ho porphyry). 

(Quartzite). 

Quartzite and indetermina¬ 
ble diorite-like porphyry. 

Diabase (?). 

(Green porphyry). 

(Siliceous limestone). 


Vein. 

Vein. 

Do. 

Vein. 
Vein. (?) 


TOOELE. 


[Note.—D eterminations in parentheses are given on the authority cf the experts.] 


CAMP FLOTD. 

* 

Stilmite, quartz, limonite, (horn-silver and antimonial 
silver). 

Limestone. 

Siliceous limestone. 

Bedded vein. 

OPHIR. 

(Limestone). 

(Limestone). 

Bedded vein. 


Gulina ceniflsite, calcite, quartz, aud limonit©_ 



Bedded mass. 


Galena, chalcopyrite, (limonite and pyrite). 



Vein. 


Galena cerussite, malachite, and limonite, (silver). 

Limestone, quartz-porphyry. 
Siliceous limestone. 

Slate dike. 

Chimneys. 
Irregular bodies. 

Bedded vein. 


(Argentiferous galena, cerussite, copper carbonates, 
native silver, horn-silver, and limonite.) 

Cernssite, horn-silver, and siliceous gangue. 

Sandstone. 


Limestone and quartzite.... 
(Clay shale, close to lime- 

Indeterminable porphyry... 
(Clay shale, close to lime- 

Mono. 

Galena, cerussite, plattnerite, (?) pyrite, (horn-silver, 

Vein. 


chalcopyrite, and limonite). 

Galena, tetrahedrite, cerussite, malachite, limonite, 
and calcite. 

Cernssite, limonite, and calcite, (the limonite is argen¬ 
tiferous). 

stone.) 

Fetid limestone. 

stone.) 

Calcareous sandstone. 

Bo. 


Limestone. 

Limestone ... 

Do. 



... do. 

Pipes. 





RUSH VALLET. 






Galena, cerussite, limonite, (manganese minerals and 
copper stains). • 

Cerussite,limonite, clay, (argentiferous galena, mala- 

(Siliceous limestone). 

(Black limestone). 

Bedded vein 

Great Basin. 

1 

1 

Limestone. 

Limestone. 

De. 

chit©, aud manganese minerals). 




























































































































































44 


PRECIOUS METALS. 


UTAH. 


[Note.— Determinations in parentheses are given on the authority of the experts.] 


---—- .■' ■■ - — - 

Ore and gangue. 

WALLS. 

Character of 

Mine. 

Foot. 

Hanging. 

deposits. 

AMERICAN FORK. 

Galena, pyrite, quartz, (silver, gold, zincblende, and 
copjjer ore). 

Galena, e.erussite, zincblende, pyrite, limonite, (silver, 
gold, and quartz). 

(Quartzite). 

(Quartzite). 

Vein. 

Live Tankee. 


Limestone. 

Do. 

Miller. 

(Limestone). 

(Limestone). 

Do. 

Pittsburgh . 

[U ilicna, LCI u^Oilo, mnwuuiV, **.aa\a / ****** ••**** - • * * 

Galena, cerussite, zincblende, quartz, limonite, arsen¬ 
ical and antimonial compounds. 

(Cerussite, pyrite, quartz, limsonite, and copper stains.) 


Limestone . 

Do. 

Wild Dutchman . 



Do. 

Treasure . 

SILVER LAKE. 





Galena, cerussite, quartz, limonite, (pyrite and zinc¬ 
blende). 

Quartzite .. 

Quartzite . 

Pipes. 

Mi 1km aid . 

(Quartzite) . 

(Quartzite) . 

Pockets. 

w ansatcn . 



- 



WAHSATCH. 

[Note.—D eterminations in parentheses are given on the authority of the experts.] 


BLUE LEDGE. 

Lady of the Lake 
Wahsatch. 

SNAKE CREEK 

Jones Bonanza. 

Pioneer.. 

Utah. 




(Porphyry). 

Vein. 



(Quartzite).. 

Da* 







Granite *.. 

Vein. 

(Galena, cerussite, limonite, copper stains, and clay).. 

(Quartzite). 

Shale. 

(?) 

Galena, cerussite, zincblende, pyrite, clay, and (tet- 

Quartzite. 

Decomposed diorite (?) * .... 

Vein. 

rakedrite). 





* Microscopically examined. 


WASHINGTON. 


[Note.—D eterminations in parentheses are given on the authority of the experts.] 


HARRISBURG. 

Buckeye . 

Magnesian clay, showing flakes of silver. Sandstone 

Sandstone and clay slate.... 

Sandstone and clay slate.... 

Bed. 

Barbee & Walker. 

with native silver and argentite. Fossil plants re¬ 
placed in part by silver and horn-silver. 

Sandstone with native silver and sulpburets, (horn- 
silver, argentite, and lignite). 

Sandstone containing horn-silver, (argentite, and na¬ 
tive silver). 

Sandstone containing horn-silver and sulpburets, 
(silver, argentite, and lignite). 

(Horn-silver, argentite, native silver, carbonized veg¬ 
etable matter.) 



Do. 

__do. 


Do. 


_do. 


Do. 


__do. 


Do. 




Do. 



_do. 


Do. 







GEOLOGICAL SKETCH OF ARIZONA. 

In the latitude of Salt Lake the Cordilleras, as Humboldt called the entire system of western North American 
mountains, occupy a breadth of over 1,000 miles. In the latitude of Tucson they are contracted to about half this 
width, which is still further reduced in Mexico. While Nevada occupies only a portion of the breadth of the Great 
Basin, Arizona, though no wider, includes a large part of the plateau region, the southern continuation of the Basin 
ranges, and probably a portion of the group of ranges of which those on the southern coast of California are 
members. The topography is thus extremely diversified and for the most part mountainous. There are fertile 
valleys and well-wooded mountains in the territory, but the prevalent character is one of great aridity, and in the 
southwestern portion there are large tracts of shifting sands, relieved only by occasional cactuses, in comparison 
with which the sage-brush plains of the Great Basin seem areas of luxuriant vegetation. Arizona is, of course, 
famous for its mines, which produce chiefly gold and silver, though lead and copper, particularly the former, are 
rather abundant, and will, no doubt, be exploited on a large scale when the railroad system is further developed. 
Coal also occurs in considerable quantities. 

A number of geologists have visited Arizona. Dr. Newberry was a member of Lieutenant Ives’s expedition 
in 1857 ; Major Powell and Captain Dutton have explored the Colorado canon and a portion of the plateaus, and 
the geologists of Captain Wheeler’s survey have contributed very greatly to a knowledge of the main features of 
the territory. But little detailed work, however, has been done in the mining regions, and such of the facts 
ascertained as are appropriate to this sketch are soon told. 




















































































































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


45 


Northeastern Arizona belongs to the Colorado plateau, of which about one-third falls within the limits of the 
territory. The Arizona plateaus are for the most part nearly level, though, as in Utah, there are folds, and even 
ranges, of uplifted mountains at long intervals. 

The southwestern limit of the plateaus is roughly indicated by a straight line running northwest from a 
point in latitude 33° 30', longitude 110°. T ' the east of this point the limiting line curves eastward, and in the 



adjoining territory of New Mexico turns toward the north. The plateau country separates two systems of ranges 
which meet to the south of it. Of these the eastern group have a northern trend and pass into the Rocky mountains 




































46 


PRECIOUS METALS. 


of Colorado. The western group trends northwest, and is continuous with the Basin ranges of Nevada. Only the 
latter ranges are met in Arizona, the most westerly of those of northern trend occurring in New Mexico just east 
of the dividing line. 

The region in which the plateaus and the two systems of ranges meet is characterized by an immense lava 
field covering between 20,000 and 25,000 square miles. 

The relations of the two systems of ranges to the plateau country and the lava fields are shown in the sketch 
map on page 45, borrowed by his permission from Mr. Gilbert’s report on the geology of parts of Arizona and 
New Mexico, to which our knowledge of the region in question is chiefly due. 

Concerning southwestern Arizona there is extremely little definite information. This portion of the territory 
is mostly composed of granites and crystalline schists, and the mountain ranges are somewhat irregular. They 
appear, however, to belong to the same structural system as those of California south of fort Tejon, with which 
they correspond in a variety of details. 

In Utah the edge of the plateau system is nearly coincident with that of the inland Cretaceous sea. In Arizona 
this is by no means the case, the surface of a great part of these elevated plains toward the west being of 
Carboniferous age, and the Triassic being largely represented on the surface. The belt of Pakeozoic included in 
the plateau country, measured from the southwestern edge of the latter, averages about 80 miles in width. The 
ranges trending northwest and continuous with those of the Great I^isin are also composed of Palaeozoic strata, 
except where the Archaean is exposed or where volcanic rocks hide the sedimentary beds. Captain Dutton’s 
investigations have established that the Jura-Trias strata formerly reached the edge of the plateau system in 
Arizona as they did in Utah, but have since been removed by erosion. This is shown by the presence of remnants 
of these beds protected by lava near the edge of the plateau, and by the impossibility of reconstructing their surface, 
except on the supposition that they reached this line. The elevation of the range system, judgiug from the analogy 
of the Great Basin, is most likely referable to the post-Jurassic disturbance which resulted in the formation of the 
Sierra Nevada. Whether the Jura-Trias beds were also raised above water-level along this line at this time is 
uncertain, but it would not be surprising if this should prove to be the case. The Cretaceous sea in Utah was 
shallow, and a slight post-J urassic elevation would have thrown its shore far east of the Wahsatch. Such a change 
of shore line may have taken place in Arizona and left the western portion of the plateau dry, or the shore line 
may have been nearly coincident with the edge of the plateau, and the Cretaceous deposits afterward removed by 
erosion, like those of the Jura-Trias. The disturbance to which the Arizona ranges is due extended eastward to the 
edge of the plateau country, and the post-Cretaceous upheaval which raised the plateaus extended westward to the 
ranges, exactly as was the casein Utah. In the northern part of the territory the contact between the Palaeozoic 
area and the crystalline rocks to the southwest of it has been traced for a long distance. This line probably lies 
somewhat to the northeast of the original edge of the Palaeozoic, but at no great distance from it. That a portion of 
these strata have been removed by erosion is indicated by the occurrence of isolated patches near the main area. 
The most remote of these is reported as occurring in the Bill Williams Fork country, and may represent a gulf in the 
Palaeozoic sea. Though the southwestern portion of the territory has not been systematically explored, it has been 
traversed in many directions by geologists who would not have failed to recognize Palaeozoic strata had they 
encountered them, and it is probable that they are absent from that region. 

The main contact between the Palaeozoic and the underlying strata is laid down in the geological maps of the 
surveys west of the 100th meridian continuously from Virgin canon to Camp Verde, a distance of 170 miles. 
Farther south the most westerly occurrences of Palaeozoic shown are in the Pinal mining district near Florence and 
in latitude 32° 20', longitude 100° 40'. These are probably near the edge of the area, though there is some evidence 
of detached patches still farther to the sofith, and to the west of the general course of the contact so far as traced. 
The Chiricahui range has been shown by Mr. Gilbert to be largely made up of Palaeozoic strata, and the mines of 
the Tombstone district are many of them sunk on deposits in limestone. In this region limestones can hardly be 
other than Palaeozoic, and they are reported as containing Carboniferous fossils. 

The rocks adjoining the Palaeozoic to the southwest are unquestionably Archaean, for their relations to the 
Silurian are clear at a great number of points, and their lithological character in this region is very characteristic 
and persistent. There seems no evidence that these Archaean rocks halve been covered at any time, except where 
comparatively small patches of the Palaeozoic have been removed by erosion near the contact. Had this area 
formed a sea bottom, like the corresponding region to the north, during the Trias-Jura, it is scarcely supposable that 
the thick sediments which must have formed should have disappeared without traces which would have been 
detected before now; and while only an elaborate field study can establish the facts, it seems allowable to suggest 
the probability that the subsidence of the Archaean, which took place at the close of the Carboniferous in western 
Nevada, did not extend to central Arizona, so that the continental area of the Trias-Jura.embraced eastern Nevada, 
western Utah, and most of Arizona, excepting the northeastern corner. The Pacific coast of that time followed the 
meridian of 117° 30' (approximately) to the neighborhood of Owen’s lake. If the supposition stated above is correct, 
it must then have left the Palaeozoic area and continued in a southerly or southwesterly direction. It appears most 
probable, on the whole, that it passed to the south of fort Tejon and out into the area at present covered by the 
Pacific. The coast in San Bernardino county, California, has no doubt slowly chauged its elevation repeatedly, but 


# 


GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


47 


Professor Whitney states that, while in that eounty a belt of 10 or 12 miles next the coast is occupied by Cretaceous 
and Tertiary strata, the region back of this is composed of granite and highly crystalline rocks of the geological 
age, of which nothing is known, (a) Such descriptions of San Bernardino county as have been published, however, 
show that the rocks are extremely similar to the Archiean of Arizona, and in the absence of definite information 
it may be assumed that they are identical. If so, there is a body of Arclicean reaching from San Diego to Camp 
Verde, a distance of about 300 miles. Its northern limit is not far from Owen’s lake, and its southern extension is 
unknown. If the shore line of the Pacific ocean in the Mesozoic era passed westward or soutliwestward from near 
fort T6jou to the present coast, Jura-Trias strata probably underlie the coast ranges in that neighborhood, and it is 
possible that they may somewhere be exposed. 

It is, of course, wholly impossible to assign a date to the Arcluean ranges of Arizona, the more so that the 
topographical maps of the area are very inaccurate. These mountains scarcely appear to form a portion of the 
Basin range system, but they may have been raised at the same time, for, though their lithological character differs 
greatly from that which prevails in those ranges, the trend and general relations of the Archman mountains 
certainly do not differ more from those of the Palmozoic ranges of Arizona than the Mesozoic Sierra Nevada from 
the ranges of the sairfe era in western Nevada. It at least seems more likely that the Archaean ranges date from 
the post- Jurassic upheaval than from either of the three other important uplifts mentioned, while it scarcely seems 
possible that any traces of a pre-Palaeozoic mountain formation should have withstood erosion till the present day 
unless protected by overlying rocks of later age. 

• Of the eruptive rocks of Arizona not much is known. Besides granite, there are enormous quantities of true 
basalt and of other volcanic rocks which have not yet been subjected to the minute examination necessary to classify 
them satisfactorily. The census collection contains numerous specimens of pre-Tertiary eruptive rocks, quartz- 
porphyry, diabase, and diorite. If the analogy of Nevada could be trusted, these rocks would be regarded as Mesozoic, 
and as probably post-Jurassic. They appear in the Palmozoic ranges, not merely as dikes, but as large masses, 
inclosing veins, and their extrusion was most likely a concomitant of the disturbance to which the formation of the 
ranges is due. Though only an examination in the field can determine the age of those mountains, the occurrence 
of these eruptives is another argument for referring them to the great Mesozoic upheaval. 

The census collection of the Pacific division contains only a siugle syenite. This forms the hanging wall of 
the Golden Eagle mine, Globe district, Pinal county, Arizona territory. A slide shows orthochise, a little plagioclase, 
hornblende, mica, and scarcely a trace of quartz. The exploration of the fortieth parallel encountered but one 
syenite. This was found in the Cluro hills, Cortez range, Nevada, and contains much more quartz than that from 
the Golden Eagle mine. The latter, however, bears a strong resemblance to the granite which is the prevailing 
rock in the Globe district, and is represented in the census collection by a large number of specimens. The Cluro 
Hills syenite is also scarcely distinguishable from the granite of the same region, and it may fairly be asked whether 
both are not to be considered as granites containing an unusually small proportion of quartz. As is well known, 
almost every fresh investigation of European syenites diminishes the number of occurrences to which the name is 
•onsidered applicable, and it seems not unlikely that it will eventually disappear from the list of rocks. 

The ore deposits of Arizona in a majority of cases are found in connection with massive rocks. Often both 
walls are granite or some later eruptive; in many cases a massive rock forms one wall of the veins, and even where 
limestone or shale entirely inclose the ore it is known in some cases that eruptive rocks occur close in the 
neighborhood. The relations of the mineral belt as a whole to the southwestern edge of the area of post- 
Carboniferous upheaval have already been sufficiently commented on. 

APACHE COUNTY. 

In the northern part of this county good coal seams exist in the Cretaceous, but at present they are little 
exploited for want of facilities for transportation. At the southern end of the county, where it adjoins Pima, 
copper ores, with blende and pyrite, occur in the veins associated with limestone and quartz-porphyry. There are 
also gold placer mines in the same neighborhood, and consequently there must be gold quartz veins, though none 
such have been reported by the experts. 

APACHE. 


Mine. 

Ore and gangue. 

. WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

COPPICE MOUNTAIN. 

Longfellow. 

GREENLEE GOLD MOUNTAIN. 

Melaconite and aznrite, zincblcnde, pyrite, with cal¬ 
careous gangue. 

Probably diorite. 


Placer. 

Coronada group. 

Malachite and cuprite, quartz gangue. 

Quartz-porphyry. 

Quartz-porphyry. 


a Auriferous Gravels, p. 18. 



























48 


PRECIOUS METALS. 


% 


MARICOPA COUNTY. 

Maricopa county includes a portion of the plateau country, and extends across the range system far into the 
Archaean area. The principal mining district in this county is the Globe, about half of which, however, lies in 
Pinal county. The principal ores are argentite and cupriferous minerals, associated with galena and zincblende. 
The ordinary gangue mineral is quartz, but heavy spar also occurs. The inclosing rocks are usually granite or 
highly metamorphosed strata, but the walls of the Mexican mine appear to be diabase. This district is nearly on the 
contact between the Palaeozoic and the Archaean. 


MAEICOPA. 


[Note. —Determinations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Charaoter of 

Foot. 

Hanging. 

deposits. 

GLOBE. 

La Plata. 

Mack Morris. 

Argentite, erubescite, and chalcopyrite; gangue 
quartz and barite. 

Copper glance; gangue quartz and barite. 

Metamorphic diorite *. 

Granite. 

Metamorphic diorite *. 

Probably vein. 

Do. 

Mexican. 

Copper-stained, (carries lead, silver, copper, and 
zinc, which on the lower levels take the form of 
sulphurets; also gold). 

Argentite, malachite, and cuprite. 

Diabase. 


Do. 

Do. 

Probably vein. 

Richmond W est. 

Granite... 


Silver Nugget. 

Vulture. 

Malachite and aznrite, accompanied by some sulph- 
arsenide of copper, (also silver and horn-silver). 

Galena, chrysocolla, malachite, stromeyerite, (gold)... 

. ..do. 

Do. 





* Microscopically examined. 


MOHAVE COUNTY. 

Mohave county lies in the northwestern corner of Arizona. The best known district is the Hualapai, 
containing Mineral Park, which lies a few miles to the west of the Palaeozoic area. The country rock of the Mohave 
county mines is almost exclusively granitic, but a gneissoid structure is said to be apparent in many cases. The 
ore occurs in veins with quartz gangue, and consists of argentite, stephanite, ruby silver, freibergite, etc., 
accompanied by galena, zincblende, and copper pyrite and mispickel. 

Near the croppings these ores are largely converted into horn-stiver and native silver, which are readily worked"; 
but at some distance from the surface most of them become very base. Many disappointments in the working of 
Arizona mines have been due not to the exhaustion of the ore, but to the fact that below the water-level the ores 
were found to be rebellious. Such ores can be worked at a profit under the prevailing economical conditions only 
when very rich. .. 

MOHAVE. 

[Note.— Determinations in parentheses are given on the authority of the experts. ] 


Mine. 

Ore and gangue. 

WALLS. 

. 

Character of 


Foot. 

Hanging. 

deposit. 

HUALAPAI. 





Cerbat. 

Quartz carrying black sulphurets and green stains, 
probably of chloride of silver. 

Galena and its products of decomposition, gangue 
quartz. 

(Granite).... 


Vein. 

Do. 

Champion. 

.... do. 


Fairfield. 



Indian Boy. 

Ruby silver, zincblende, galena, and chalcopyrite. 



Do. 

Keystone. 

Galena, zincblende, and chalcopyrite and pyrite, 
quartz gangue. 

Ruby silver and indeterminable black sulphuret stains; 
quartz gangue. 

Galena and cerussite with quartz gangue. . .. 

(Granite).. 


DO. 

Lone Star. 



DO. 

Pure Metal. 

(Granite).. 


DO. 

MAYNARD. 




Do. 

American Flag. 

Galena, stephanite, argentite, zincblende, and iron 
and copper pyrites, (freibergite, native silver, and 
mispickel), quartz gangue. 

Galena and colorados; quartz gangue. ... 

(Granite). 


Vein. 

Do. 

Do. 

Peabody. 



Hackberry. 

(Silver chloride, argentiferous galena, and antimonial 

_do. 



silver; quartz gangue.) 




* Microscopically examined. 







































































































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


40 


Hualapai district is very large, ami contains a number of mineral neighborhoods. At Chloride veins occur in 
granite with quartz gangue. Near thesurface the ore minerals are carbonate of lead and silver chloride. Below the 
water level these are replaced by galena and pyrite. The mines mentioned are: Schenectady, Schuylkill, Empire, 
Juno, Silver Hill, Pinkeye, Kanawha Belle, Oriental, and Porter. Near Stockton deposits are found which are 
similar to the foregoing, but they are reported as containing also native silver and ruby silver, as well as zincblende, 


chalcopyrite, and some stibnite. The mines mentioned are: Indian Boy, I. X. L., Tiger, Ed. Everett, Cupel, 
Dolly V., Pure Metal, Little Chief, Prince Geo., and Tigress. At Mineral Park native silver and silver chloride 
occur near the croppings of the veins which carry a quartz gangue and are inclosed in granite. The undecomposed 
minerals are argentite, ruby silver, stephauite, with some galena and zincblende, iron pyrite, and arsenical pyrite. 
The mines mentioned are: Keystone, Lone Star, Fairfield, Quick Belief, Conner, and Metallic Accident. At 
Cerbat the ore thus far mined carries horn-silver in a quartz gangue, with some native gold and silver, complex 
sulpharseuides, and antimonides and zincblende. The mines mentioned are: Cerbat, Black-and-Tan, Snowflake, 
Mocking Bird, Sixty-Three, Falstaff, Fontenoy, Champion, New Loudon, Flora, and Paymaster. 

The Maynard district, like the Hualapai, shows quartz veins in granite and mineral associations similar to that 
last mentioned. The mines reported are: The American Flag, Peabody, Dean, Antelope, and Mississippi. 

The Cedar Valley district is also in a granite country. The ores are argentiferous galena, ruby silver, tetrahedrite, 
and, near the croppings, horn-silver, accompanied by zincblende, pyrite, and quartz. The mines mentioned are: 
Silver Queen, Hibernia, Hope, General Lee, Arnold, Billy Engle, Eainbow, Eugenie, Bunker Hill, Congress, 
and Gunsight. 

Owens district is in a granite country, but a portion of the rock is gneissoid. The ores are argentiferous galena 
and argentite, with decomposition products near the croppings and a quartz gangue. The mines of the McCracken 
company aud the Signal mine are the chief ones of the district. 


PIMA COUNTY. 

This county occupies the southern end of the territory, and crosses the mineral belt. It contains a very large 
number of districts, the most famous of which is Tombstone. Many of the mines in this district are in limestone, 
and carry chiefly argentiferous lead ores. Manganese minerals (pyrolusite and wad) sometimes accompany them 
in large quantities. There are also veins in the Tombstone district in quartzite. These carry cupriferous minerals 
more or less charged with silver and some free gold. 

From mine reports and papers by Professor W. P. Blake it appears that the ore in the Tombstone district 
occurs in Palieozoic beds, probably of Carboniferous age, which have a prevailing inclination to the north and 
east, resting on a granitic base, which outcrops some distance to the southwest. These beds consist of a fine¬ 
grained quartzite, called by him novaculite, about 140 feet in thickness, underlaid by a light-colored dolomitic 
limestone and overlaid by a blue-black limestone passing into shaly beds. The principal portion of the ore is 
found at the horizon of this blue-black limestone. The sedimentary formations have been compressed into a series 
of sharp folds and fissured and traversed by dikes of pre-Tertiary eruptive rock, known in the district as diorite. 
The census collection from Tombstone contains both diorites and diabases. The general direction of the fissures and 
dikes lies between north and northeast. The ore occurs both in fissures which cross the strata either parallel to 
or in direct connection with the dikes and ijj bodies branching out from these approximately vertical bodies in a 
inore horizontal direction, following in general the bedding planes of the formation, whose prevailing dip is to the 
northeast. The ore is most abundant and richest in that part^of the black limestone beds which are contiguous to 
the quartzite, and the vertical fissures generally contract and become less rich where they cross the quartzite itself. 
Their continuation in the lower limestone beds has not yet been much explored. In the origin and manner of 
deposition of its ore bodies the district would seem to resemble that of Chauarcillo in Chili. 

There are also veins in the granite, or associated with it, near Tombstone, which are similar to the other 
deposits of the territory found in this rock. The group of districts, including .the Oro Blanco, Arivaca, Harshaw, 
etc., just north of the Mexican line, seem to possess much the same character as Tombstone. The country rock 
is granite, limestone, quartzite, or earlier eruptive rocks, and the ores are galena and its products of decomposition, 
ordinarily accompanied by copper minerals and charged with silvfcr. They are sometimes auriferous. In the 
western part of the county there are gold and copper mines, with some lead ores. These are sunk on veins in 
granite, which carry, besides quartz, fluorite and heavy spar as gangue minerals. 


vol 18-4 



50 


PRECIOUS METALS. 


PIMA. 

[Note.—D eterminations in parentheses are given on the authority of the experts.] 


WALLS. 


Mine. 


Ore and gangue. 


Foot. 


Hanging. 


Character of 
deposit. 


AUIVACA. 

Consolidated Arizona. 


I 

Coppe r stains and LLcksulphurets in small quantities, Quartz-porphyry ... 
with quartz and barite, (also chlorides and carbon¬ 
ates). 


Quartz-porphyry 


DOS CAMEZAS. 


Juniper 

Murphy 


The ore shows blue stains, which are possibly horn- 
silver, (freegold and horn-silver), gangue quartz and 
liniunite. 

(Free gold and lioru-silver), gangue quartz and limo- 
uite. 


llAltSHAW. 


Hrriuosa 
Holland . 


AV. C. Davis . 

HABTFOHD. 
AVisconsin .. 

At EVE lift. 


Shale. Shale 


(Sedimentary). \ (Slate) 


Vein. 

Vein. 

Do. 




Kaolin and manganese oxides, (carbonates). j Quartzite. J Quartzite. 

Ceiussite and cupriferous minerals, (zincblende, ga- Limestone. Limestone. Pockets. 

lena, end antimonial mineials, gangue quartz, and 
limestone). 


Cerussite, (galena, gangue quartz).| Granite ’ 


Malachite, (horn-silver), gangue hematite 


Atlanta. 


Westward 
Gunsight . 


MULE PASS. 

Co; per Queen. 

QUO BLANCO. 


A laska 
Li>ugarina . 


n.iua-- 


(Granite) 


Gab na,-cerussite, copper stains, gangue quartz, fluo¬ 
rite, and heavy spar. 

Galena, gangue quartz. 

Galena, horn-silver, copper stains, gangue quartz, 
barite, and hematite. 


Malachite, gangue quartz, and calcite. Slate and limestone 


Limestone . 


.do 


Do. 


— do ... 
Granite 


Do. 

(Granite) 

_do- 

Granite.. 


Vein. 

Do. 

Do. 


Nor; h Pacific. 
W.;i saw. 


PIMA. 

Kspi ranza. 

S.-n Xavier. 

SWISS HELM. 

V. : moth and Whale. 

Qn en. 

TOMBSTONE 

Bradshaw. 


Content iuu 

In:.-rail. 

Empire . 

Grand Central 

Grand Dipper . 

Head Center .. 

Mamie __ 

Monitor. 


Itattk snake. 


Malachite, (carbonates with copper and lead). j Quartz-porphyry. 

Galena, cerussite,malachite; possibly stephaniteand Quartz conglomerate . 
horn-silver, quartz gangue. 

Cerussite, gangue quartz, and limonite.■ Conglomerate. 

(Gold), gangue red quartz . .! Granite’ 1 . 

Galena, freibergite, and ehalcopyrite, (carbonate near j Diorite *. 

surface), gangue quartz (calc-spar). 


Galena, pyrite, and ehalcopyrite, gangue kaolinite .. Probably diabase" 
Galena and ehalcopyrite, gangue quartz.! Limestone. 


Slate and limestone,. j Vein 

Quartz-porphyry. j Vein. 

Quartz conglomerate. Do. 


Utterly decomposed 

Granite*. 

Diorite *. 


I 


Do. 

“ Flat." 
Vein. 


Cerussite, gangue quartz, limonite .! Limestone ... 

Galena and cerussite, (gangue calcareous).|_do. 




Probably diabase *. Vein. 

Limestone. j Connected pockets 


Limestone.| Connected pockets. 

_do. Do. 




Gal-tin, cerussite, malachite, cln\ socolla, and proba- Indeterminable.; Indeterminable.. 

bly mime! ite, (horu-bilver). gangue clay, (quartz). 

Cerussite, (horn-silver, gangue calcite).i.; Probably quartz-porphyry. .|. 


Malachite, (bora-silver), gangue, quartz, and calcite.. Black limestone. Black limestone 


Mctaruorpkic *. Limestone .. 

Sandstone. (Sandstone). 


(Horn-silver), gangue quartz and limonite. 

Minute specks of black sulpliurets, (horn-silver and 
ceiussite), gangue quartz and limonite. 

Horn-silver, malachite, and ehiysocolla,* (gangue 
quartz and calcite). 

(Gold and h(ti n-silver), gangue quartz and limonite... 

Angle-site and cerussite. (horn-silver and copper stains). 

Cerussite and horn-silver, (free gold), gangue calcite, 
limonite, (manganese minerals). 

Cerussite, (horn-silver), gangue iron oxide, (quartz I Black limestone.! Black limestone 

and calcite). 


Solfatarically - decomposed j. 

eruptive rock. 

Quartzite*. j Quartzite*. 

— do .|_do. 

-do .. j _do. 


Bed Top. Cerussite and bora-silver, (free gold), gangue limo- ! Quartzite 

nito, and calcite, (quartz). 

Stonewall. j (Chloridesand carbonates), gangue, pyrolusite. 


Sulpliuret.j Cerussite, (chloride and carbonate, gangue calcite)... 

Sunset,.| (Chloride aud carbonate), gangue, \ftkl, (iron oxide).. 

Tioga.i (Free gold and trace of silver), gangue, ferruginous 

quart z. 

Toughnut Extension. | (Chloridesand carbonates),gangue, ferruginous quartz. 

Tonghuut and Goodenougb.. Cerussite, (horn-silver and copper carbonate), gangue, Limestone, decomposed dio- 

limonite, and fluorite, (quartz and limestone). j rite, (and quartzite). 

True Blue. 


Quartzite.. 
Limestone. 


Limestone .. 

Diabase. ,j Diabase... 

Limestone. J Limestone 

Quartzite. 


Granite.... 

(Porphyry for 100 feet), lime¬ 
stone iu part siliceous. 


TUUQIJOISE. 


Defiance 
A jo. 


(Horn-silver), gangue, limonite, and pyrolusite.; Diabase* 


Galeua and ceiussite, (very little silver), gangue, quartz Limestone . 
aud limonite. 

Chalcopyrite, bornite, and malachite, gangue frag- i Quartzite 
ments of rock. 


(Porphyry for 100 feet), lime¬ 
stone iu part siliceous. 

Limestone, decomposed dio¬ 
rite, (and quartzite). 

Diabase*. . 


Limestone . 
Quartzite.. 


Connected pockets. 

Do. 

Do. 

Do. 

Do. 

Vein. 

Do. 

-Do. 

Do. 

Probablyvein. 

Vein. 

Pockets. 

A r ein. 

Do. 

Do. 

Do. 

Pockets. 

Vein. 


A 7 eiu. 

Probably vein. 


Microscopically examined. 































































































































































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


51 


PINAL COUNTY. 


Most of the miues of this county are found in the northeastern portion, near the edge of the Palaeozoic. The 
ores are argentite and the sulphantimonide minerals, often associated with lead ores, commonly also with those 
of copper, and sometimes accompanied by zincbleude. The gangue minerals are quartz, calcite, occasionally 
manganese compounds, and sometimes (in granite) heavy spar. Limestone, slate, sandstone, and quartzite, as well 
as granite, diabase, and diorite occur as wall rocks. Cupriferous minerals are less apt to be associated with 
limestones than with other metamorphic rocks or granite and diabase. The famous Silver King mine is in the 
Pioneer district in this county, and its great yield is a sufficieut refutation of the statement sometimes made that 
large deposits of good ores do not occur in granite, for the country rock of this mine is a typical granite, though 
locally called syenite. A very great number of ore minerals occur in the Silver King, the specimens showing native 
silver, stephanite, freibergite, ehalcopyrite, erubescite, stromeyerite, copper carbonates, galena, and zincbleude. The 
gangue is quartz accompanied by barite. Half of the Globe district occurs in Pinal county. Its characteristics 
have already been mentioned under Maricopa. 

PINAL. 

[Note.—D eterminations in parentheses are given on the authority of the experts.) 


Mine. 


GLOBE. 

Golden Eagle. 

Irene..*. 

K. C. McCormick. 

Silver 1 Era. 

Stonewall Jackson_ 

PIONEER. 

Silver King. 


Surprise! 1 .. 
El Capitan 


Ore and gangue. 

WALLS. 

• 

Character of 

Eoot. 

Hanging. 

deposit. 

Galena, limonite. and malachite; quartz and pyrite 
gangue. 

Syenite*. 

Syenite *. 

Vein. 

(Carbonates, some lead, and a little arsenic), gangue, 
psilomelane, quartz, limonite, and chlorite. 

Quartz-porphyry*. 

Sandstone. 

Do. 

Copper stains and speckswhich are probably stromey¬ 
erite, (chloride); gangue quartz, probably manga¬ 
nese. 

Quartzite. 

Slate and limestone. 

Do. 

(Sulphides and chlorides), gangue psilomelane and 
quartz. 

Quartzite and slate. 

Quartzite and slate. 

Do. 

Stromeyerite, gangue kaolinized rock. 


Granite. 

Do. 




Native silver, freibergite, stephanite, zincblende, 
ehalcopyrite, erubescite, malachite, azurite, galena, 
and stromeyerile, gangue quartz and barite. 

Granite*. 

• 

Granite*. 

Vein. 

(Gold and carbonates), gangue quartz, probably man¬ 
ganese minerals. 

Quartzite. 

Limestone and slate. 

Do. 

Galena, polybasite,ruiargyrite.pyrargyrite, andchalco- 
pyrite, ('stephanite, argentite, and zincblende) ; 
gangue calcite and (quartz). 

Diorite and slate. 

Diorite and slate. 

Do. 


*,Microscopically examined. 


YAVAPAI COUNTY. 


The mining districts of this county are chiefly in its southwestern portion, near the edge of the Palteozoic 
area. There are some gold quartz veins in granite and granite-porphyry in this couuty, and silver veins occur 
under similar conditions. It seems not improbable that the relations of these two classes of veins are the same as 
in Idaho, but this cannot be asserted without further information than is now available. Most of the deposits, 
however, are veins in metamorphic rock carrying lead and copper minerals as well as silver. Heavy spar occurs 
as a gangue in the Silver Belt mine, gneiss or granite forming the hanging wall. 

YAVAPAI. 

[Note.—D eterminations in parentheses are given on .the authority of the experts.) 


Mine. 

Ore and gangue. 

WALLS. 

Character of 

Foot. 

Hanging. 

deposit. 

BIG BUG. 

Galena and cerussite, ( oxides and chlorides), gangue 
barite and calcite. 

Gold quartz, gangue quartz, and iron. 

Pyrargyrite, zincblende, and pyrite, (chlorides on the 
upper levels), gangue quartz. 

(Carbonates and chlorides, galena and antin oi.y, 
gangue quartz, iron oxide, and calcite.) 

Galena, cerussite, and copper stains, (chlorides), 
gangue (country rock). 

Galena, zincblende, and pyrite; gangue quartz. 

Metamorphic. 

Metamorphic. 

Granite. 

Vein- 

CHERRY CREEK. 

Granite. 

Vein. 

HUMBUG. 

Granite.... 

Gneiss. 

Vein. 

PECK. 

Slate. 

Quartzite. 

Vein. 


_do. 

... do . 

Chimneys. 

Vein. 

TIGER: 

Tiger . 

Gianite. 

Granite. 


- 

-- 

— 

-. 





































































































52 


PRECIOUS METALS. 


YUMA COUNTY. 


Most of the mines of this county arc near the Colorado river. They are sunk on quartz veins in highly 
metamorphic rocks or granite. The William Penn and other mines in the Castle Dome district are associated with 
a greenstone, which proves under the microscope to be diorite. The ores of Yuma county are chiefly silver ores, 
accompanied by lead minerals. Fluorspar and heavy spar are found in many of the veins'which are inclosed in 


giamte. 


YUMA. 

[Note.—D eterminations in parentheses are given on the authority of the experts. 1 


Mine. 

CASTLE DOME. 

Flora Temple. 


WALLS. 


Ore and gangue. 


Foot. 


Hanging. 


Character of 
deposit. 


(Argentiferous galena and anglesite), gangue, (flu¬ 
orspar, calc-spar, quartz, and gypsum). 

Galena Chief. (Ore same as above), gangue, fluorspar, and calcite... 

Norma. Galena, cerussite, and anglesite, gangue fluorspar 

« | and calcite. 

I’ocahoiitas . Same as Norma.. 

William Penn...do.. .. 


Gneiss, slate, and diorite*.. Gneiss, slate, and diorite*.. 1 Vein. 


SILVER. 




i’rincess. ! Galena and eemssite, (argentite and horn-silver), I Gianiteand micaceous slate, 

gangue, calcite, (quartz, fluorspar, and barite). j capped with conglomerate. 

lied Cloud. Cerussite, anglesite, and horn-silver, gangue, manga- Granite. 

nese minerals, iron oxide, quartz, fluorite, barite. 

Hover.I Gangue, calcite. 


Same as foot wall. 

Hornblende-andesite.* 


Vein. 




* Microscopically examined. 

IDAHO TERRITORY. 

General character of the territory.— Idaho lies in the northeastern corner of the Great Basin, directly 
southwest of the Bitter Root mountains. The southern portion of the territory resembles the regions farther south, 
its southwestern portion forming a continuation of the Nevada sage-brush deserts and the southeastern corner 
being the northern end of the sandy and alkaline deserts of western Utah. The upper branches of the Snake 
river, the sources of which are in the Yellowstone park and the Tdton range, just east of the Idaho line, unite 
about 50 miles west of that boundary. For a shoit distance from the junction the course of the river is nearly 
south, but it bends gradually westward and northward, reaching the Oregon line on a northwest course. The area 
south of the Snake river is about one-fourtli of the entire territory. The valley of the Snake is a plain from 50 
to .100 miles in width, which is occupied by a vast sheet of recent basalt from the Wyoming line to Owyhee county. 
Immediately to the north of this plain, which lias an elevation of a little over 4,000 feet, the character of the country 
changes abruptly, and most of the rest of the territory is extremely mountainous, many of the summits rising to 
between 10,000 and 12,000 feet above sea-level. The climate changes with the topography. Central and northern 
Idaho are east of Oregon and Washington territory, to the coasts of which the trade-winds of the Pacific bring an 
enormous amount of rain. The coast is, indeed, separated from the northern portion of the Great Basin by .the 
Cascade range, but this is much lower and much less continuous than the Sierra Nevada to the south. The 
westerly winds thus bring a greater amount of moisture to northern Idaho than to Nevada, while the lofty peaks 
of the northern area promote its precipitation. To the north of the Snake River region Idaho is consequently well 
watered and well wooded, conditions of the utmost importance to profitable mining. On the other hand, the winters 
are long and severe, and lines of communication are extremely circuitous. 

Except in the eastern counties, no portion of Idaho has been submitted to systematic geographical or geological 
survey, and the maps of the territory are very inaccurate. The geological information furnished by the census 
examination is necessarily fragmentary, presenting only data from a large number of mining localities, and but little 
assistance can be derived from any local publications with which I am acquainted. The following paragraphs, 
therefore, contain only a very rude outline of the geological conditions of the mining regions of Idaho. 

A very large granite area occupies a portion of southwestern Idaho. It appears to be oval iu shape, its longer 
diameter extending from a few miles south of Yankee fork nearly to the South Mountain district, while its shorter 
diameter reaches from the common boundary of Washington and Boise counties in a southeastern direction to the 
Wood River country. Its total area is probably about 12,000 square miles. Not all of the country within this oval 
area shows granite on the surface, for Ada county is largely alluvium, and Palaeozoic limestones are reported as 
occupying much of the more northern portions; but the extremely frequent occurrence of granite, for the most part 
of a single type, appears to justify the supposition that the body is continuous under the later formations. 

The granite from the Idlewild mine, Carson district (Silver City), Owyhee county,is a soft gray rock with rather 
well developed crystals of white mica, cleavage flakes of which give the biaxial interference figure of muscovite. 
Slides show nndci the microscope that (lie constituents arc ortlioclase, oligoclase, quartz, and mica, with a little 









































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


53 


apatite and magnetite. The quartz is extremely full of fluid inclusions, many of them containing moving bubbles. 
The sti ucture is the ordinary one of granite; indeed, the rock is quite typical. In the same district occur excellent 
quartz porphyries, slides of which show dihexahedral quartz crystals, with the characteristic association of glass 
and fluid inclusions. The association of these two rocks suggests a similar origin, or, in other words, that the granite 
may be eruptive, but of course proves nothing. On the other hand, there is no known evidence tending to show a 
derivation of the granite from sedimentary rocks. The granite from the Sub Rosa mine, in the Bois6 basin, is in 
most respects similar to that from Carson district, though about 80 miles distant from it, but contains biotite in 
addition to the muscovite. In several localities in the territory the granite is extremely coarse-grained, and has even 
furnished marketable mica sheets. 

The granite has been profoundly disturbed by eruptive action, and probably at a comparatively recent date. 
The evidence of this is manifold. Dikes of eruptive rock, among which the principal one appears to be basalt, (a) 
are common in the granite, and as basalt appears everywhere to be the youngest of the lavas this would indicate 
comparatively recent action. Hot springs, too, are thickly distributed through the granite area, in many cases 
issuing directly from the granite, though usually within a mile or two of known occurrences of volcanic rocks. 
This is most naturally accounted for by supposing that there are still remnants of volcanic heat at great 
depths below r the surface. A further and most interesting point bearing upon the structural geology of the region 
and the age of the disturbances is the fact that the very numerous veins found in the granite usually strike in the 
direction of the ranges on the flanks of which they occur. The fissures which these veins occupy must have been 
formed by an upheaval such as would produce these ranges, and it seems necessarily to follow that the mountains 
are substantially a result of upheaval, and not of erosion. This upheaval, too, must be comparatively recent in a 
geological sense, say as late as the Tertiary, since otherwise the results of upheaval would have been obscured by 
subsequent erosion. The occurrence of the immense.lava fields of the Snake River valley immediately adjoining 
. the granite area suggests that the dynamical disturbances and the thermal action manifested in the granite may be 
a portion of the same series of phenomena to which the Snake river eruptions are due. The age of the veins 
themselves is quite another matter. The facts mentioned indicate a possibility that the ores have been deposited 
after the upheaval which determined the present topographical character of the country; it may be through the 
agency of the solfatarie action (b) accompanying the basalt eruption. Indeed, the numerous hot springs of the 
granite area are in many cases highly charged with alkalies and sulphhydric acid; in short, they are solfataras. 
They often occur in the immediate neighborhood of the mines, one of the mining districts in the Wood River country 
even bearing the name of the Hot Springs district. In a mineral region solfataras, active or extinct, are usually 
associated with ore deposits, which are commonly ascribed to their action, and it is difficult to see how the period of 
solfatarie activity now drawing to a close can have failed to give rise to metalliferous concentrations in Idaho. 

On the other hand, the structure of the country is not incompatible with the supposition that the veins are far 
older than the basalt and a concomitant of a former disturbance of the granite. Fissures in the earth’s crust, once 
formed, seem never to heal, and faults have occurred at the present day on surfaces upon which movements are 
know'll to have taken place in the Paheozoic era. The recent upheavals may merely have followed old lines of 
movement which had been marked by veins long before the present mountains rose. An indication tending to 
such a view is the fact that some veins are faulted, though this is not the rule, w'hile slickeusides, showing relative 
motion of the walls of the veins subsequent to the deposition of ore, are very abundant. While known movements 
of a more recent date thau the ore deposits are thus shown, the extent of these movements usually appears to be 
small. Much the strongest evidence of older veins is furnished by the placers of Boise basin and the canon of 
Moore’s creek, a little below and south of the basin. There is, of course, every reason to suppose that auriferous 
gravels are accumulations from the croppings of veins. They do not represent the whole material eroded from a 
country, but only the heavier portion which the streams have been unable to carry to great distances. The gravels 
of Boisd basin are estimated to cover 30 square miles to an average depth of about 12 feet. This large mass 
represents not merely a very extensive erosion of the upper country, but streams of a size inconsistent with the 
present rainfall of the territory. It does not follow, however, that the general character of the topography of the 
country must have been altered by this erosion to such an extent as to obscure the relation of the strike of the 
veins to the trend of the ranges. Not only were these gravels deposited when the climate was much moister, but 
they date from a time prior to some of the basalt eruptions, for in Moore’s creek, the outlet of the Bois6 basin, the 
gravel, which is continuous with the main deposit, is covered by a basalt cap which can scarcely be younger than 
the Snake River bed. 

hi the light of the present knowledge of the country, it seems on the whole most probable that the greater part 
of the quartz veins of this region are of Cretaceous or possibly Tertiary age, but it is by no means unlikely that a 
part of them are subsequent to the basalt, and thus are of very recent date. Should this be established by future 
investigations, it would afford a remarkable instance of the repetition of certain chemical and physical conditions 
at considerable intervals in geological history. 

a As (lie eruptive rooks* arc nol immediately associated with the ore deposits in any of the mines visited, specimens of this basalt 
were not collected. 

h See note to page 6. 






54 


PRECIOUS METALS. 


A very large portion of the mines in Idaho are within the granite district, and are sunk upon veins between 
granite walls. These veins are very similar to those in the other granitic mining districts of the Great Basin. 
They are numerous and rich, but narrow, being seldom above 3 feet in thickness, though there are a few w ide 
veins, as, for example, the Atlanta, Middle Boise district, Alturas county, which is from 50 to 75 feet across. The 
gangue of the veins in the granite area is quartz, accompanied by more or less decomposed granite as horse matter. 
The ores carry both gold and silver iu very varying proportions. The gold is either free or is mechanically entangled 
in pyrite, mispickel, or zincblende, while the silver appears near the surface as chloride, and at lovei le\eK .is 
sulphide, stephanite, tetrahedrite, or as ruby silver. Zincblende appears occasionally, and galena still more rarely. 
Tn some veins gold greatly predominates, in others silver; yet the association of minerals is the same in both classes, 
the relative quantities only of the two precious metals varying. There is nothing to show that the two classes ot 
veins are of different origin or age; on the contrary, every gradation between the two extremes occurs, and 
sometimes both are represented in the same vein. On the Atlanta lode the Buffalo and Monarch mines pioduce 
about twice as much silver as gold, while in the Yuba tuunel, more than a mile distant from the others, but on the 

same lode, the value of the ore is almost wholly in gold. 

From a geological point of view there is little to note concerning the variations ot the ore deposits ot the 
granitic area without going into more detail than this chapter is designed to record. On the contrary, the most 
striking point connected with this area is the great similarity from one end to the other ot the inclosing rock and 
the included deposits. As soon as the water-line is passed suites of specimens from the various mines are almost 
indistinguishable, except in point of richness. In prospecting for these veins it would be w r ell to observe not only 
the float, the character of the croppings, and the like, but also evidences ot disturbance, and particularly 
decomposition of the country rock, for both of these phenomena are likely, though not certain, to accompany the 
presence of ore. 

The uniformity in character of the veins throughout the granite area of Idaho, in spite ot a possible difference 
in age and their dissimilarity to.those characteristic of other formations, is highly suggestive of the nature ot their 
origin. It is almost certain that the ores of veins are precipitated from solutions, and that these solutions acquire 
their valuable contents either at great depths and from unknown sources, or from the rock masses adjoining the 
place of deposition. The latter supposition, which is known as tile lateral secretion theory, has been gaining 
ground of late years, and it has been proved in many cases to satisfy all the known facts. Of granite in particular 
Professor F. Sandberger has shown that the mica frequently carries various heavy metals, and he has pointed out 
an exceedingly probable series of reactions by which these metals may have been concentrated in veins. In the 
granite of Carson district, Owyhee county, Mr. A. Simuudi has detected gold (usually amounting to at least 25 


cents per ton), besides silver, even at long distances from any known deposit of ore. In view of Sandberger’s 
investigations, it is improbable that this content is due to impregnation from veins. 

If it be supposed that the Idaho veins are due to metalliferous solutions rising from great depths, it would be 
necessary to assume that the granite has had a chemical influence on the precipitation; for if this were due merely 
to reduction of temperature and pressure, the differences between the deposits in granite and those in the other 
rocks of the territory would be inexplicable. But the Idaho granite appears to be Archaean, and the lower surface 
of the Archaean has never been reached in any part of the world. Whatever may underlie it, it is certainly 
enormously deep. It would therefore be also necessary to assume that the granite exerted little or no precipitating 
influence at great depths and pressures, but only within a certain, no doubt large, distance from the surface; for 
were the precipitating action vigorous toward the lower portion of the granite the solutions would, for the most 
part, be robbed of their metallic contents at a depth of miles. If this were the case, ore veins, if reached at all, 
would grow T richer and stronger as lower levels were attained. If any rule can be established in regard to the 
relations between richness and depth, it is rather that veins grow less rich and strong, though strong veins, 
probably as a rule, continue metalliferous to a greater depth than mining can ever be carried ; but the cases in 
which veins grow better in proportion to the depth reached are certainly very exceptional. 

On the other hand, so far as the facts concerning the veins iu granite iu Idaho are known, the supposition that 
they are the result of a leaching of the granite itself, probably by heated waters, appears simple, satisfactory, and 
sufficient. It would account for the difference between the veins in granite and those in other rocks by the 
difference in the rocks themselves, and place the source of the ores in the neighborhood of their present position. 
Whether any actual particle of ore originally formed a constituent of the granite on the same level or a few 
hundred feet below, or even above, no one would of course venture to assert. The hypothesis is merely that the 
rock in the neighborhood of the-veins has furnished their contents. 

Interesting and in part extremely important ore deposits have been discovered in the sedimentary rocks 
adjoining the granite area, and, indeed, on all sides of it. It has been asserted that a portion of these deposits form 
a continuous mineral belt. So broad a statement can hardly be indorsed, but there is sufficient evidence to warrant 
the assertion that the zone of country immediately surrounding the granite is well worth prospecting with unusual 
care, and that valuable smelting ores are not unlikely to be met with at almost any part of this zone at or near the 
granite contact. 


GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


55 


1 In* most southerly <>t this class of deposits are those of the South Mountain and Flint districts, in Owyhee 
county, near the Oregon line. 1 he country rock is chiefly limestone, and the ore argentiferous galena. No work was 
done in these districts during the census year or for some time before, not, it is stated, on account of lack of ore, but 
in consequence of financial embarrassments arising from the failure of the Bank of California in San Francisco in 
1S75. lo the northwest ot the granite lies the Heath district, in which rich galena, high-grade copper ores, iron, 
and lignite are reported. No description of the country rock has been published, and as the district was idle during 
the census year the census examination did not include a visit to it; but the association of minerals leaves little 
doubt that the area is sedimentary. In the Yankee Fork district, north of the granite, the country appears to 
consist ot gneiss (a) and eruptive rocks, while the ores show gold and silver, but seem to carry more copper than 
in the granite district. The important Custer mine is in this locality. In the Bay Horse district slates are 
accompanied both by milling and smelting ores, lead and copper being often prominent constituents. Both this 
and the preceding district were visited by Mr. Williams in the depth of winter, when work on almost all the 
mines was stopped, and it was impossible to obtain entirely satisfactory suites of specimens. 

I he Wood River country lies southeast of the granite area. Limestone, slate, and granite are the prevailing 
rocks, and argentiferous galena (or its products of decomposition), often extremely rich, is the chief ore. As is so 
usually the case with galena, the ore bodies are irregularly distributed in limestone, but the true meaning of this 
association has never been fully explained. Mr. Emmons, in discussing the Leadville deposits, regards the galena 
as precipitated by substitution for the limestone, but no one as y r et has indicated the probable chemical reactions 
involved. Milling ores also occur in the Wood River country in the granite and slate. This region was opened up 
during the census year, but has since acquired great importance. The geographical distribution seems to indicate that 
a relation exists between these lead bearing districts and the granitic area about which they lie. It is altogether 
probable that the ore w r as deposited throughout the whole region at the same time or times, and that the 
differences in the character of the ore are attributable to the different chemical and physical characters of the rocks. 
Were the galena deposits all on one side of the granite it might well be maintained that they were wholly 
independent of the gold-quartz veins in the granite, but any r hypothesis which will account for them independently 
in their actual distribution appears extremely artificial. 

Besides the deposits which have been mentioned, there are also veins carrying precious metals in Warren’s 
camp, in the northern part of Idaho county. The ores from this camp are quartzose, carrying free gold and ores 
of silver. The association much resembles that met in the mines of the great granite area, and the country rock 
is also reported by Mr. Wolters as granite. Gold mines also occur at Iowa bar, in the extreme eastern portion of the 
territory. Limestone and ‘‘porphyry” are said to be the accompanying rocks. Lignite has been found in various 
portions of Idaho, for example, in the valley of Boise river and on Reynold’s creek, in Owyhee and Oneida counties, 
etc., but uo commercially valuable deposits have as yet been discovered. Sulphur occurs in connection with hot 
springs in Bear Lake county, and deposits of alkalies exist in the same portion of the territory. Considerable 
quantities of float cinnabar have been found in Stanley basin, at the eastern extremity of Boise county, and along 
t he Salmon river between the mouth of Yankee fork and the town of Sawtooth, but not in place. Cinnabar is usually 
associated with Cretaceous rocks on the Pacific coast, and this tact might be of use in the search for the ore if the 
horizons of the neighborhood had been identified. Tinstone has been found as wash in the bed of the Jordan river, 
Owyhee county. This is one of the few points at which tinstone has been encountered in the far west, Temescal, 
San Bernardino county, California, and Deer Lodge county, Montana, being the principal other localities. 

The auriferous gravels of Idaho are of great volume and extent. Though of much less importance than those 
of California, they have been more productive than those of any other state or territory except Montana, and have 
probably yielded something like thirty million dollars’ worth of gold. 

Three distinct classes of auriferous gravels may be recognized in Idaho. The bars of the Snake river are 
auriferous, but the gold is in an extreme state of division, and can be recovered at a profit only in exceptional 
cases. Many rich but small placers occur along the banks of the Salmon and of the other rivers of Idaho, and 
were either deposited by the present streams during freshets, or left by a comparatively slight shifting of the 
channels. Small placers have usually been found near the croppings of gold veins, which have undoubtedly 
furnished the auriferous gravel, and a large part of the veins, as in California, have been discovered by tracing 
these gravels to their sources. Most of the richest of the small placers have probably been worked out; at least 
few new ones of remarkable value have been discovered for many years ; but enough is left to furnish occupation 
ro a considerable population. The deep gravels of Boise basin are of a different character. The basin is surrounded 
except at one point by mountains, and receives no drainage from beyond its own limits; yet it is estimated to 
contain Lome 125,000,000 cubic yards of auriferous gravel, and some of it has a depth, it is asserted, of no less than 
250 feet. While there is evidence of a channel in a northeastern and southwestern direction, the gravels spread 
over nearly the whole basin, and occur even on the tops of considerable hills. The gravels extend several miles, 
dow T n Moore’s creek, the outlet of the basin, and are here, in part, covered by a heavy basalt cap. The pay-dirt is, 


a A slide of the country rock of the Charles Dickens mine shows a structure usual in highly metamorphic rocks, corresponding to. 
its microscopical appearance, hut the constituents are so thoroughly decomposed that little more can be said of it. 



PRECIOUS METALS. 


5 b 

commonly near the bed-rock of these beds, as is usual elsewhere. Large bowlders are frequent, as aie also fossil- 
tree stems, which are so characteristic of the auriferous gravels of California. The Boise basin deposits are not 
worked out, though their yield has decreased during the last few years, owing, it is said, rather to high wages and 
lack of water than to dearth of good gravel. In the earlier days of mining in Boise basin many extremely rich bars 
were found, which were undoubtedly concentrations from the older gravels by modern streams. Few, if any, of 
these rich spots can have escaped the eager search which has been made for them. It would be impossible to 
account for the presence of the gravels of the Bois6 basin at the head of a system of drainage without a special 
examination undertaken for the purpose, but it may be considered certain that a great river once flowed through the 
basin and transported the gravel. Some secular or paroxysmal action, not improbably a concomitant of the basalt 
eruption, must have modified the topography in such a way as to deflect this river, but the character of the change 
in the drainage is unknown. The Bois6 basin gravels were probably contemporaneous with those of California; 
for the present rainfall, as has already been pointed out, is insufficient to account for them, and it is not probable 
that greatly increased precipitation can have prevailed in either of two districts so similarly situated as California 
and Idaho without its being shared by the other. The fossil plants also seem to be the same or extremely similar, 
as are also the relations to the basalt. 

The following sections of gravels are selected out of a considerable number to illustrate their occurrence. 
The third of these is noteworthy as an exception to the ordinary rule that the pay-dirt lies near the bed-rock. 

CREPISCULLA HYDRAULIC MINE. 


MOORE’S CREEK DISTRICT, BOISE COUNTY, IDAHO (SECTION IN NORTH WORKINGS). 


I 

II 

III 

IV 

Brown soil. 

Uniform low-grade gravel of medium size . 

Bowlder stratum (quartz and granite). 

Bed-rock granite; hard when first uncovered, slacking rapidly on exposure. 

2-3 feet. 1 

47 feet. Maximum. 70 feet. 

10-20 feet. ) 

1 

f None absolutely barren, but the bulk 
< of the gold is thought to come from 
( the lowest quarter of the bank. 

The bank shows a fine section across the riverbed 550 feet wide, which is now left at the summit of a low.bill. This part of the claim is from 350 to 450 feet 
higher than the south workings. 

Ii. W. SPENCER’S HYDRAULIC MINE. 

BOSTON, BOISE COUNTY, IDAHO. 

I 

II 

m 

Loam, with some small quartz bowlders. 

Quartz, gravel, and clay, with small bowlders not over 9 inches in diameter, 
chiefly -granite. 

Bed-rock; soft, decomposed granite. 

3 feet, j Maximum, 10 feet; average, 

3 feet. 5 3 * feet - 

< Grass-root gold. Color throughout 
) deposit. Best pay on bed-rock. 

NOBLE, LOWER & MANN HYDRAULIC MINE. 

MOORE’S CREEK DISTRICT, BOISE COUNTY, IDAHO. 


I 

II 

III 

IV 

Soil. 

Quartz, gravel, and clay. 

Rotten bowlders of quartz and granite, 9 inches to 4 feet in diameter. 

Bed-rock granite; very rough, hard when first uncovered, but slacking 
rapidly on exposure. 

• 

2 feet. - 1 

I Maximum, 30 feet; 
2-6 feet. , average where work- 

10-15 feet. J ing. 15 feet. 

) Upper 3 feet from surface is the pay - 
1 ing portion. 


Riverbed 300 feet wide and 2,000 feet long on claim. The bowlder stratum, III, is too poor to pay for wording by itself, but all has to be piped off to obtain 
grade for race—one-fifth good pay and lower four-fifths low grade. 


SUMMARY BY COUNTIES. 

Ada county.— There is very little -mining in Ada county, the principal industry being agriculture. The 
occurrence of galena not far from the granite area of the adjoining counties, however, is an interesting fact, though 
no work was done in the Heath district, where it occurs, in the census year. 

Alturas county.— The western portion of Alturas county, together with Boise county, forms a great granite 
district, chiefly drained by the Boise river and its tributaries. The veins in this granite carry a quartz gangue, with 
gold and silver ores. In some the one metal predominates, in some the other, but as a rule both are present. The 
ores are free gold and auriferous pyrite, native silver, both ruby silver minerals, steplianite, freibergite, liorn-silver, 
and galena. The gangue minerals are quartz, pyrite, clialeopyrite, mispickel, zineblende, and a little calcite. 
Molybdenite is also reported. .Nearly all the veins dip at an angle of over 45°, and the majority strike northeast 
and southwest, following the trend of the mountain ranges. 

To the southeast of the granite, in the Wood River country, there are deposits in limestone of galena and its 
decomposition products, accompanied by copper and iron minerals. Milling ores are said to have been found in 
the slates of this region since the expiration of the census year. There are also small placer deposits on the Salmon 
river and its tributaries in this county. 
















































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


5 ' 


ALTURAS. 


[Note.— Determinations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 

Foot. 

Hanging. 

deposit. 

BONAPARTE. 





Bonaparte Consolidated. 

(Gold, galena, antimony, argentiferous sulpbarsen- 
ido and sulphanlimonide minerals, zincblende, 
pyrite), quartz, and oalcite. 

(Gold), quartz.. 

Granite. 

Granite. 

Vein. 

HARDSCRABBLE. 

Crown Point Bonanza. 

(Granite) . 



Emma. 




Do. 

Do 

Do. 

General Grant. 

Gold quartz and limonite. . 

....do. 

.. do .. 

New Ophir. 

Gold quartz, pyrite, mispickcl, galena, and (zinc- 
blende). 

Ruby silver, quartz, pyrite, chalcopyrite, (arsenical 
and antimonial silver- ore, with auriferous pyrites). 

(Dark and light ruby silver, native silver, auriferous 
pyrites, and quartz.) 

.. do .. 

...do 

MIDDLE BOISE. 

Jessie. Benton. 



Buffalo. 

.. do. 

_do. 

Do. 




Buffalo and Atlanta. 

(Auriferous pyrites, argentiferous sulpharsenides 
and sulphaniimonides, quartz, and molybdenite.) 

.. do. 

. do.. 

Do 

Last Chance. 


... .do. 

Do. 

Do. 

Do. 

Monarch. 

Dark ruby, horn-silver, native silver, quartz, pyrite, 
and probably mispickel, (light ruby, auriferous 
pyrites, free gold, and traces of copper-). 

Argentite, an argentiferous sulpbarsenide, quartz, 
(ruby silver, native silver, and a little free gold). 

(Gold), quartz, feldspar, pyrite, and mispickel. 

Rich argentiferous galena.. 

Granite. 

Granite. 



...do . 

Yuba Tunnel. 

MINERAL HILL. 

Idahoan. 

(Limestone). 

(Limestone). 

Jay Gould. 

Galena and cerussite. 


Do. 


queen's river. 







Granite . 

Granite. 


Mammoth. 

Quartz and galena, (native silver-, free gold, light 

(Granite) . 

(Granite) .. 

Do. 

Silver Glance. 

and dark ruby silver-, and auriferous pyrites). 

Quartz and galena, (stephanite, native silver, light 

-do .r_ 

.. do . 

Do. 


ruby silver, pyrite, and a little gold). 

_do . 


Do. 

RED WARRIOR. 

Quartz color-ado, (gold, pyrite, antimonial'ores. No 
silver). 

(Granite). 

(Granite).. 

* 

Vein. 


_do. 


Do. 




.. do . 

Do. 

Wildcat. 

Quartz and mispickel, (gold and silver in rebellions 

-do. 

....do . 

Do. 


compounds). 

... .do.. 


Do. 

ROCKY BAR. 

Gold quartz pyrite, aud mispickel. 

Granite. 


Vein. 


Gold galena quartz, pyrite, aud mispickel.. 

.... do. 

... do. 

Do. 





SAWTOOTH. 






Quartz, probably horn-silver and freibergite, (rulTy 
silver). 

(Granite) . 

(Granite). 

Vein. 


_do. 

.. do.. . 

Do. 

Luekv Boy..’ — 

Quartz and horn-silver... 


... do.-.... 

Do. 


Boise county.— This county is, for the most part, in the granite area mentioned under Alturas county. The 
veins carry chiedy gold, except in the Banner district, where the silver is in excess. The placer deposits of this 
county have hitherto been the most important in the country outside of California. Their character and occurrence 
have already been sufficiently described. 

































































































































58 


PRECIOUS METALS. 


BOISlS. 

[Note— Determinations in parentheses are given on the authority of the experts.] 


Mine. 

Ore and gangue. 

WALLS. 

Character of 
deposit. 

Foot. 

Hanging. 

BANNER. 






A sulpharsenide of lead, probably dufreynoysite, 
quartz and pyrite, (ruby silver, horn-silver, mis- 
pickel, sulphur, and copper compounds). 

Quartz, (ruby silver). 


Granite dike. 

Vein. 

• 

1‘anamint .. 

Granite. 

Granite. 

Do. 

CANON CREEK. 



Granite . 

Vein. 

Ebenezer. 

Gold quartz, iron and copper pyrites, and mis- 

Granite. 

Granite. 

Do. 

GAMBUIXU6. 

piekel. 

. 

Granite *. 

Granite* . 

Vein. 

GRANITE. 

Gold Hill 


Granite. 

, 

Granite. 

Vein. 

MOORE’S CREEK. 




Placer. 


.do. 

... do. 


Do. 

SIIAW’S MOUNTAIN. 




North Star. 

Gold quartz. 

Granite. 

Granite. 

Vein. 


(Gold) quartz. 



Do. 





Rising Sun. 

Gold quartz, galena, copper, pyrite, and probably 

Granite. 

Granite. 

Do. 


mispickel, (ft®® sulphur). 





* Microscopically examined. 




Idaho county.— This county appears to contain an isolated granite area in the neighborhood of Warren’s 
camp and Florence. The quartz veins are much the same in character as those in Boise county, and are 
accompanied by small deposits of auriferous gravels. 


IDAHO. 


[Note.— Determinations in parentheses are given on the authority of the experts.] 


Mine. 

■ 

Ore and gangue. 

WALLS. 

• 

Character of 
deposit. 

Foot. 

Hanging. 

WARREN’S CAMP. 

Various mines .. 

Gold, native silver, horn-silver, sulphurets, and 
quartz. 

(Slate and limestone) . 

(Slate and limestone). 

Vein. 


Lemhi county— The important mining districts of Yankee Fork, Mount Estes, and Bay Horse lie in the 
southern portion of this county. In the Yankee Fork district the principal rocks appear to be gneiss and an eruptive 
which is possibly rhyolite. (The workings were superficial, and the specimens were too much decomposed for 
determination.) Free gold and silver minerals are accompanied by quartz, pyrite, and copper ores. In the Bay 
Horse district the country rock is slate, and the ore consists of argentiferous galena, with copper minerals and traces 
of gold in a quartz gaugue. 

LEMHI. 


[Note.— Determinations in parentheses are given on the authority of the experts.] 


Mine. 


HAY HORSE. 
Kamshorn. 

YANKEE FORK. 

Charles Dickens. 

General Custer. 

Unknown. 


Ore and gangue. 


(Argentiferous galena, gray copper, a little chloride 
and bromide of silver, copper carbonates, traces of 
gold, hematite and quartz.) 


Iron and copper pyrites and melaconite, (gold). 

Quartz, pyrite, and probably stephanite, (argentite). 


Same as General Custer. 


WALLS. 

Character of 

Pool. 

Hanging. 

deposit. 

(Slate). 



Metamorphic*. 

Metamorphic. *. 

Vein. 

Indeterminably decomposed 

Same as foot wall. 

Do. 

yellow porphyry (locally 
called rhyolite). 





Do. 




Microscopically examined. 






























































































































GEOLOGICAL SKETCH OF THE PACIFIC DIVISION. 


59 


Owyhee county. —The mining districts of Owyhee comity lie about Silver City and Wagontown, on the 
Jordan river. This region is separated from the granite region of Alturas and Boise counties by the Quaternary 
plains of Ada county, but it is extremely probable that the granite of Silver City is a portion of the larger mass 
to the north. To the southwest of Silver City the surface is occupied by quartz-porphyry overlying metamorphic 
rocks in part, and both porphyry and granite are intersected by dikes of basalt. The ores are similar to those of 
the northern granitic area: gold, silver, freibergite, and sulphurets in a quartz gaugue. The veins follow the general 
trend of the mountains to the northwest and dip at high angles. As usual, small placers accompany the gold veins. 

In the South Mountain district, near the Oregon line, galena occurs in limestone. Coal has been found, but 
only in insignificant quantities. Tinstone has been identified as float in the Jordan river. 

OWYHEE. 

[Note.— Determinations in parentheses are /riven on the authority of the experts.] 


Mine. 


CARSON. 

Black Jack.. 

Clearbrook . 

Empire . 

Florida Hill. 

Idlcwild. 

Owyhee . 

Potosi. 

Ruth. 

War Engle. .. 

WAGONTOWN. 

Bismarck. 

Last Chance. 

Maggie ... . 

Ohio. ... 

Tremont. 

W ebfoot. 


WALLS. 


Ore and gangue. 


Quartz, and probably argentite, (gold and horn-silver) 

Quartz, horn-silver, and probably argentite, (gold, 
calc-spar, copper stains). 

(Free gold and argentiferous sulphurets, quartz). 

Gold, quartz, liiuouite. 

Quartz, horu-silver, (some gold)... 

(Free gold and argentiferous sulphurets, quartz)_ 

Finely divided sulphurets uot determinable, quartz .. 
Probably argi ntite, quartz . 


(Free gold and argentiferous sulphurets, quartz) 


Foot. 


Hanging. 


Character of 
deposit. 


Metamorphic.. Quartz porphyry*. Vein. 

Muscovite granite . Muscovite granite. Do. 


(Granite) 


(Granite) 


-i 


Do. 


(Muscovite granite)*. (Muscovite granite)*. Vein. 

_do .. .. . .. do .. . . Do. 

Granite. ' Granite ... Do. 

Granite of somewhat gneis- Granite of somewhat gneis- Do. 
soid structure. j soid structure. 

(Granite). (Granite).. Do. 


I 


Gold, quartz, and limonite. (Porphyry). 

Gold, quartz, and limonite. Quartz-porphyry... 

Similar to Tremont and on same vein, not specifically (Quartz-poiphyry) 
determinable, quartz, 

Argentite, quail z, (gold, pyrite, and antimony). (Porphyry). 

Stephanite, quartz, and kaolin. (Quartz-porphyry). 

Quartz, (gold, low grade). (Porphyry). 


(Porphyry) . 

Quai tz-porphyry . 
(Quartz-po’ pbyry) 


(Porphyry). 

(Quartz-porphyry) — 
(Porphyry) ... i. 


Vein. 
Do. 
Do. 

Do. 
Do. 
Do. 


Microscopically examined. 


OTHER COUNTIES. 

In Oneida county gold quartz veins and placers are worked at Cariboo and Iowa Bar, and along the course of 
the Snake river in this and Cassia counties gold washings are conducted on a small scale. 

The northern couuties of Kootengi, Nez Perce, Shoshone, and Washington contain gold quartz veins and 
placers, which are not, however, worked to any considerable extent, and the conditions of their occurrence are not 
known. 

Salt and sulphur are obtained in Bear Lake county. 






































































60 


PRECIOUS METALS. 


Chapter II —GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION 


By S. F. Emmons. 

In the following pages the writer has endeavored to present a brief outline of the geological structure of the 
states and territories of this division as far as it bears on the ore deposits of the region, the geological occurrences 
of the ore deposits themselves, and their mineralogical composition as far as it has been possible to determine them. 
Such a sketch at the present time must, from the nature of things, be extremely unequal, and, at its best, very 
incomplete; but it has seemed best to give it in this incomplete form, even if it merely serves to show the gaps 
in our knowledge and to encourage others to fill them up. The importance of the geological relations of mineral 
deposits has been hitherto very much underestimated, chiefly for the reason that so few competent men have given 
attention to their study. For this reason geological literature contains but little trustworthy information on this 
subject. 

The material here presented has been in part compiled from data and specimens gathered by census experts, 
and in part from reports of government surveys, from reports by individual geologists upon mining districts, 
unfortunately too few in number, and from the personal observations of the writer in portions of Wyoming and 
Colorado. There was difficulty in obtaining men who had at the same time a knowledge of field geology and a 
practical acquaintance with mines, and the limited time at the disposal of those to whom the work was intrusted 
rendered it practically impossible to visit every mining district. Of the specimens of ore, gangue, and country 
rock which it was intended should be obtained from each mine a large proportion were in a too far advanced 
stage of decomposition for satisfactory determination. In many cases no specimens accompanied the schedules. 
Hence the tables of mines, country rocks, and ores which accompany the following sections are incomplete in 
many important instances; but it has not been thought advisable for that reason to refrain from publishing them, 
even in their imperfect condition, since they contain many data useful to mining engineers, and will serve as a 
skeleton which may hereafter be more completely clothed as additional material is obtained. In cases where no 
specimens were at hand it is indicated in the table, the information given being on the authority either of the 
experts themselves or of some person connected with the mine. At the end of another decade it is hoped that our 
knowledge of these important mining regions will be such as to render it possible to present the information which is 
here outlined in a comparatively complete form. 

The maps which accompany these sketches are intended as a guide to the reader unacquainted with tlie 
geography of the country, and will serve to show those who are already somewhat familiar with it the county 
divisions, which have been followed in the treatment of each section. An attempt has also been made, in a very 
general way, to indicate by colored dots the relative distribution among actually producing mines of ores in which 
gold or silver predominate. These are given, as well as the rest of the material, rather as a sketch than as a finished 
and accurate delineation. 

GEOLOGICAL SKETCH OF COLORADO. 

The state of Colorado, which is included between the 57tli and 41st degrees of north latitude and the 25th and 32d 
degrees of longitude west from Washington, has an area of 103,045 square miles. This area may be divided into 
three meridional belts: a plain belt, comprising a little over one-third of the eastern portion of the state; a 
mountain belt, lying next west of the former, and covering also about one-third of the state; and a narrower belt 
on the west, which is largely a mesa country, and belongs to the so-called Colorado plateau region. 

According to the classification of Lieutenant Wheeler’s maps, only about one-fifteenth of the whole surface is 
arable land, but at the time this classification was made probably only the alluvial bottom lands of the larger 
streams were assumed to be available for agricultural purposes. This restriction may hold good for the mesa region, 
but with the late rapid increase in the population of the state increasing areas of plain country to the east of the 
mountains have been brought under cultivation by means of irrigating ditches, and the results obtained have shown 
that the soil is exceptionally favorable to agriculture, the extent to which it can be profitably carried on being 
probably limited only by the feasibility of irrigation. A large portion of the plain country is covered by a porous, 
crumbling, homogeneous soil, filling irregularities of the rock surface beneath to depths of from 5 to 20 or more 
feet, whose external appearance strongly resembles that of the famous loess which has proved the source of 
fertility of many important agricultural regions in the world. 

As yet no systematic studies have been made of the geology of the plain country, and the actual extent and 
character of this deposit is not definitely known. It seems probable, however, that it may at least be analogous 



GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION 


61 


to the loess which has been proved to exist farther east, in Nebraska and Kansas. An analysis of this soil, 
taken from the neighborhood of Golden, close to the foot-hills of the mountains, made in the laboratory of the United 
States geological survey at Denver, gave the following results: 

• . Per cent. 

Silica..,. 72.312 

Alumina. 12.604 

Sesquioxide of irou. 4.609 

Lime. 1.147 

Magnesia. 0.944 

Potash. 3. 748 

Soda ..;_ 2.472 

Water and organic matter .... 1 . 797 

Phosphoric acid ...7. 0.228 

99.981 


The lime and magnesia in this soil are in considerably smaller proportions than in ordinary loess soils, but at 
least 50 per cent, of the material may be supposed to be free quartz. It may be assumed, therefore, that at a greater 
distance from the mountains the proportion of silica will be smaller, and the more soluble and easily transportable 
salts greater. The same soil about 10 miles to the east of Denver, or 20 miles from the foot of the mountains, 
yielded 4.5 per cent, of lime and 0.8 per cent, of magnesia in a soluble form, probably as carbonate. 

The climate of Colorado is essentially a dry one, though less so than that of New Mexico. In summer there 
are often showers, but they are too uncertain to be depended on for agricultural purposes. 

Artesian wells. —The extent to which agriculture may be carried on is therefore dependent mainly upon tin* 
amount of water which is available for purposes of irrigation. The various streams which emerge from the mountains 
yield a sufficient supply for a comparatively narrow belt along the foot-hills, but, owing to the rapid evaporation 
which takes place in this dry climate, they cannot be counted on for irrigating the lands at any great distance to 
the eastward. 

Artesian wells have been suggested as another source of supply, and government aid has been called in to 
make practical experiments, with a view to determining whether these wells will yield water in sufficient amount for 
purposes of irrigation. The water supply of artesian wells is supposed to follow the laws of hydrostatic pressure; 
that is, where the surface water, penetrating the earth from the surface, reaches an impermeable stratum, it follows 
the inclination of that stratum as an underground stream. If, then, this stratum be reached by an artesian boring 
at a point where the surface of the ground is sufficiently below the outcrop of that* stratum, the water, seeking its 
original level, will flow out through this boring to the surface. The structural conditions on the great plains are 
theoretically favorable for obtaining flowing wells. The sedimentary formations w hich underlie them are upturned 
at their western edge against the foot-hills of the mountains, and are thus accessible to the waters'which drain their 
surface. The surface of the plains slopes regularly to the eastward, although at a very gentle angle; so that to 
obtain the required difference of level it will be necessary to go some distance from the mountains, as it is found in 
practice that the water from artesian wells does not strictly fulfill the condition of finding its own level, but that a 
certain portion of the difference of elevation is lost probably by friction and the want of a perfectly free underground 
circulation. Of the sedimentary formations the Tertiary beds lie horizontal and are not upturned, and these, owing 
to their porous character, probably would not carry the required supply of water. It is advisable, therefore, to avoid 
sinking the wells where these still exist, and fortunately their present area is probably limited. Of the Mesozoic 
beds, the upper formations (the Cretaceous) are largely composed of sandstones, which are also porous and more or 
less permeable to water. They contain also, it is true, beds of clay, but it cannot be certainly stated that these 
clay beds are continuous over any great areas. It is questionable, therefore, if the Cretaceous formation will yield 
a large supply of water, except locally, as near Denver, where a synclinal basin is formed by a slight fold in the 
strata to the east of it. In the Jura, below the Cretaceous, the conditions seem more favorable, as they'contain 
a considerable amount of clay and a comparatively persistent limestone bed. The Trias is a formation largely 
of sandstones, and therefore not favorable, and it is only when the Carboniferous is reached, which is made up of 
compact and evenly-bedded limestone, that wo come to strata which are beyond doubt capable of carrying the 
required supply of w r ater. The thickness of these different formations has not yet been accurately determined; but 
it may be assumed at the foot-hills that the Cretaceous beds are at least 3,000 feet in thickness, and the Jura and 
Trias 2,000 more. Tt will be seen, therefore, that it may require a boring 5,000 feet in depth to give a permanent 
and considerable flow of water. On the other hand, there are good grounds for supposing that the thicknesses of the 
different formations decrease to the eastward, and this supposition has been in part confirmed by actual observation 
along a line near the southern border of the state. It is probable, therefore, that at a sufficient distance to the. 
eastward the thickness of the beds overlying the Cretaceous formation will be very much less than the figures above 
given. In the present state of our knowledge these are largely matters of conjecture, and it is only by the actual 
experiment of boring wells that the thickness and water-bearing properties of the different formations can be 
determined. It is evident, however, from what has been said, that these experimental weIN should be sunk near 
the eastern border of the state, and at points where the greatest thickness of the upper beds is likely to have 














PRECIOUS METALS. 


G2 


been removed, bringing the deep-seated water-carrying bed, therefore, nearest the present surfaces. To deteiinine 
these points with accuracy, however, would require an accurate and systematic topographical and geological sui\ t }, 
which lias not yet been made, and the choice of the right location must be largely a matter of chance. It seems 
probable, therefore, that with its exceptionally favorable conditions of climate and a soil of this character the 
agricultural resources of Colorado are yet but partially developed. 

Coal — Its industrial possibilities, if gauged by its natural resources in coal, the indispensable basis of almost 
every industrial enterprise, are almost unlimited, not less than two-thirds of the areaof the state being underlaid by 
the coal formation. While over a great portion of this area it may lie too deep for profitable extraction, and while 
coal beds are by no means necessarily continuous in any particular formation over very large areas, yet the geological 
conditions are such that a relatively large proportion of this formation is brought to the surface and rendered 
available for practical working, especially along the borders of the mountain belt. Along the eastern front coal 
mines are already opened and working at intervals from the northern to the southern boundary of the state. 
Mines are also worked in the South park, in the center of the mountain belt, and in Gunnison and La Plata 
counties, on the western slope, while the developments in many other localities are only awaiting railroad 
communication and an industrial demand. 

Mountain belt. —The precious-metal production of the state is derived mainly from the mountain belt, as 
might have been assumed on a priori geological grounds, reasoning from which none would be looked for in the 
plain country : nor would much be expected from the mesa region, except where eruptive rocks have protruded 
through the sedimentary strata and formed such isolated mountain groups as the Sierra la Sal, Sierra Abajo, 
Sierra el Late, and others. The topography of the mountain region and the plateau country on its west, as well 
as its general geological structure, is pictured on the maps of the Hayden survey, of which the extreme northern 
strip is taken from those of the Fortieth Parallel. The most important group of rocks there represented, and 
intimately connected with ore deposition, viz, those of Mesozoic or Secondary age, have either entirely escaped 
recognition or have been classed indiscriminately as belonging either to the volcanic rocks or to granites. 

The mountain belt of Colorado, which in this latitude is generally known as the Pocky mountains, to distinguish 
it from the other principal Cordilleran systems to the westward, the Wahsatch and the Sierra Nevada, has, taken as 
a whole, a due north and south trend. When examined in detail, however, it is found to be made up of a number of 
more or less regular chains or ridges having a general trend to the west of north, standing en echelon or with their 
ends overlapping each other, with mountain valleys of greater or less extent between them, as the result of which 
structure the mountains in general seem to be divided up into two chains, with large included valleys which have 
received the name of “parks”. The general name of Colorado, or Front, range has been given to the eastern of 
these divisions, and that of Park range to the western. The North, Middle, and South parks and the San Luis 
valley are the larger of the included valleys, the three former, with the smaller Wet Mountain valley to the south, 
being really a portion of the same continuous line of depression, while the valley of the Upper Arkansas stands 
in the same relation to the San Luis valley. The eastern front of this range presents a comparatively regular north 
and south line, broken here and there by bay-like valleys, running up into the mountains in a northwesterly direction 
and following the prevailing trend of the echelon ridges. The most important of these are the Manitou and Huerfano 
parks and that which extends up Oil creek from Canon City. These in earlier geological times were actual bays 
in the seas in which the Palaeozoic and Mesozoic rocks were deposited, while the parks were partially inclosed 
arms of those seas. 

The western front of the mountains is, however, much more irregular, and is broken by branching mountain 
groups extending out, also with a general northwest trend, into the mesa country of the Colorado plateau. The 
principal of these outlying mountain groups, commencing on the north, are the Elk Head mountains, the White 
River plateau, the Elk mountains, and the San Juan mountains, in all of which, as will be seen later, there is a very 
great development of eruptive rocks. 

Geology.— The geological history of this mountain region is, briefly and in its most general outlines, as follows: 
At the close of the Archaean era, or in the Cambrian ocean, a large area, covering most of what is now the Colorado 
range, formed a large rocky island, with a number of minor islands lying to the westward, the most important of which 
was that which now forms the Sawatch, from which it was more or less completely separated by the waters occupying 
the present depressions of the North, South, and Middle parks. During the whole of the Pal.eozoic and Mesozoic eras 
a continuous sedimentation went on in the seas surrounding these islands of material derived from their abrasion. 
The geological record, as far as it has been studied at the present day, gives evidence of no great disturbance during 
this long period, although it is probable that local elevation and subsidence might have taken place; and there is 
some evidence to show a general subsidence of the whole area, which gave a somewhat larger field of deposition to 
the later sediments of these periods. Toward the close of the Cretaceous period, at the time of the formation of the 
coal beds, the seas became shallower, owing to a general elevation of land, and considerable portions of the outlying 
areas were partially inclosed. During this time, and possibly earlier, immense masses of eruptive rock were forced up 
through the already deposited sediments which were still beneath the water. LFnlike the lava flows of modern 
days, however, these molten masses were not, as a rule, spread on the surface of the rocks, but congealed before 
they reached it, either in large masses, in dikes, or in sheets spread out between the beds. It is impossible to say 


63 


GEOLOGICAL SKETCH OF THE 


ROCKY MOUNTAIN DIVISION. 


how long 1 before the close of the Cretaceous period the eruption of these Secondary igneous rocks commenced, but 
it is known that iu certain localities it must have continued nearly to the close of the period. At some time after 
the close of the Cretaceous period a general dynamic movement took place in the Rocky mountains, by which the 
existing mountain ranges or islands were crushed together, broken, and elevated, and considerable areas of the 
adjoining sea bed were lifted above its surface. In the general continental elevation which followed freshwater 
lakes or inclosed seas were formed, iu which, by the degradation of the newly-made land areas, considerable 
sediments were deposited. The outlines of these Tertiary seas, owing to the nature of the deposits made in them, 
which were easily eroded and carried away by subsequent atmospheric agencies, cannot be yet definitely determined. 
It can only be said that their area and location were frequently changed, and that during the Tertiary era, and 
subsequent to it, eruptions of igneous rock occurred, generally following the lines of earlier eruptions, but, unlike 
those, spreading out on the actual surface of the land, and in some cases beneath the sea. While the general 
form of the mountain area, as has been shown, was determined in the very earliest geological times, it is only 
since the Tertiary era, and in a great measure by erosion subsequent to the Glacial period, that the present 
sculpturing of the mountain forms and carving of the valleys have taken place. At what period during this history 
the different mineral deposits of Colorado were formed it is as yet impossible to say with any degree of definiteness. 
Tlie gold deposits of Gilpin county in the Archaean may, like those of the Black hills of Dakota, be of pre- 
Cambrian age. It is probable, however, that some of these at least, and the silver deposits in the adjoining counties 
of Clear Creek and Boulder, were subsequent to the intrusion of the porphyries, which are presumably of later date. 
The silver deposits of Leadville are known to have been formed subsequent to the Carboniferous and previous to the 
dynamic movement at the close of the Cretaceous. Some of the silver deposits of Gunnison, on the other hand, 
must have been later than the Cretaceous, while those of Custer county and the San Juan region are in part at 


least presumably of post-Tertiary age. 

Ores. —The ores of Colorado present an almost infinite variety of miueralogical composition, so that it is difficult 
to formulate any general laws with regard to their distribution or manner of occurrence. Of the actual precious- 
metal production of the state, by far the largest portion is derived from pyrites and galena and their decomposition 
products. The telluride ores of Boulder county and the auriferous pyrites of Gilpin county, with a few individual 
deposits in the southern portion of the state, constitute the source from which its gold is derived. With these 
exceptions its mineral deposits may be considered as essentially silver-bearing. The principal source of silver, as 
has already been stated, is argentiferous galena and its decomposition products, while argentiferous gray copper, 
or freibergite, is next to this the most important silver-bearing mineral. The sulphides of silver also occur, and 
iu some cases bismuth is found in sufficient quantity to constitute an ore. As yet, so far as known, no copper is 
extracted from the ores of the state, except as an adjunct in the reduction of silver-bearing copper ores. Placer 
deposits are generally confined to the valley bottoms among high mountain ridges, and while they are locally of 
considerable value and importance, and were the original attraction which brought the mining community to the state, 
their present yield forms a very inconsiderable proportion of its precious-metal production. Prior to the discovery of 
the silver o~es of Leadville mining in the state was principally confined to approximately vertical veins either in the 
Archaean rocks of the Front range or the eruptive rocks of the San Juan region ; but since the limestone deposits of 
the Mosquito range have proved so exceptionally rich the attention of prospectors has been more and more turned 
to the ores which occur in sedimentary rocks, and many new districts have been discovered, but none to rival that 
of Leadville. 

As regards geological distribution, gold is found in the Archaean and in the eruptive rocks of the Secondary age. 
In the sedimentary formations it is comparatively rare in limestone beds, but is not infrequent in siliceous beds. 
Silver is also found in the Archaean and in the Secondary eruptive rocks. In the sedimentary beds, on the other 
hand, it is more common in the limestones, although it is not exclusively confined to them. By far the greater 
portion of this metal produced iu the state is derived from the limestones of the Palaeozoic formations. 

The most important generalization to be made with regard to the distribution of ore deposits is one that has 
been already noted in other countries, viz, that the largest and most important ore deposits are found where igneous 
rocks are most abundant. The experience of the writer leads him to further modify this by saying that it is the 
eruptive rocks of earlier age than the Tertiary volcauics with which valuable ore deposits are generally associated. 

The mineral wealth of the state is by no means coufiued to the precious metals. Its coal beds are widespread, 
and contain both bituminous and anthracite coals. Gypsum beds are of frequent occurrence iu the Triassic and 
Upper Carboniferous formations, and salt springs are not infrequent, and probably derive their supply from the same 
horizon. The Dakota group of the Cretaceous on the eastern foot-hills carries beds of most remarkably pure fire¬ 
clay. Excellent building-stone is quarried from the Arclnean, which furnishes red granite; from the Mesozoic 
formations, which furnish white and red sandstones and valuable fiags; and from the tufaceous rliyolite-lava beds 
of the plains. 


04 


PRECIOUS METALS 


EASTERN COUNTIES. 


Weld, Arapahoe, Elbert, and Bent counties, and the eastern portion of Las Animas, lie entirely in the plain 
region east of the mountains. Their surface is covered to a depth of from 10 to 20 feet by a light, porous, almost 
loess-like soil, which is admirably adapted to agriculture wherever it is possible to bring water for purposes of 
irrigation. Where this is not possible, the natural grasses are most valuable for the raising of stock. No metallic 
minerals are to be looked for in this region, but it is underlaid by the rocks of the coal formation, which must contain 
extensive and valuable beds of this mineral, whose development is only dependent on the market demands and the 
depth below the surface at which it occurs. 


LARIMER COUNTY. 

This county includes the northern end of the Colorado range in Colorado, and, although mostly a mountain 
district, has as yet developed no considerable mineral wealth. One reason of this may be found in the fact that 
the range is here mainly made up of Archaean granite—a coarse, red, crumbling rock, which is characteristically 
developed at Sherman, on the Union Pacific railroad, and which has in this state thus far proved barren of 
metallic minerals. A further reason may be found in the comparatively limited development of Secondary eruptive 
rocks, which, so far as known, occur only in the western limits of the country bordering on the North park, at the 
head of Grand river. Mines have already been discovered near the western boundary of the county, at the 
head of Laramie river, in the Medicine Bow rauge. 


GRAND COUNTY. 

This county includes the North and Middle parks, whose surface is mainly covered by Mesozoic rocks, and 
are separated by a cross-range of eruptive porphyry and volcanics. In the Archtean mountains which inclose the 
county, and still more in the eruptive range which divides the two parks, the geological conditions are favorable 
for the formation of valuable deposits of minerals. As yet, howevei>owiug to the difficulty of access and want of 
railroad connection, no important mines have been developed, and data from the few mining districts that exist 
within the county are entirely wanting. The coal-bearing formations originally covered the greater part of both 
park areas, but these have been removed in part by erosion. 

ROUTT COUNTY. 

This county, which extends from Grand county west to the Utah line, comprises the valleys of the Yampa and 
of the Little Snake rivers, which are underlaid by coal rocks, whose deposits come to the surface along the borders, 
but in the centers are too deeply buried beneath the overlying Tertiary beds to be practically available. 
These deposits, as elsewhere, afford no promise of metallic minerals. In the bordering mountains the only known 
mineral developments are the placer mines of Hahn’s Peak district, which are found in the angle between the 
Archtean uplift of the Park range and the volcanic group of the Elk Head mountains. These placer deposits are 
evidently derived from the disintegration of Archtean rocks, and have yielded a small but constant return for 
many years past. Near the junction of the Elk river with the Yampa is an extremely interesting group of mineral 
springs carrying sulphur and free carbonic acid, known as the Steamboat springs. The coal-bearing Cretaceous 
formations occupy the valley of the Yampa river and a great part of the ridge which divides it from the White 
river on the south. Favorably situated outcrops are abundant, and only await the advent of railroads to become of 
practical value. 

BOULDER COUNTY. 


Topographical. —The mines of Boulder county are situated on the eastern slope of the Colorado or Front 
range, not far from the town of Boulder, which lies at the mouth of Boulder canon where it debouches on the plains. 
The district containing the mines extends about 13 miles in a north and south direction, and from 4 to 10 miles from 
east to west. 

The country is drained by a number of creeks, which cut deep canons between the mountain spurs. These are, 
commencing on the north, the south branches of Saint Yraiu creek, then James (popularly Jim) and Left-hand 
creeks, which joiu a little below Jamestown and flow out on the plains, as Left-hand creek, into the Saint Vrain at 
Longmont; next the various forks of Boulder creek (Four-mile, North Boulder, and Middle Boulder), which flow 
past the town of Boulder in a single stream, and also are tributary to Saint Yraiu creek. 


The town of Boulder is connected by the Colorado Central railroad with Denver on the south and Cheyenne 
on the north, and by the Boulder Yalley railroad with the Denver Pacific railroad. A narrow-gauge railroad is 
also projected from Denver to run up into the mountains via Boulder. There are a number of small mining districts 
in this region whose limits were not definitely ascertained, but they are not in themselves important, except for 
purposes of description. The mines on the Saint Vrain are generally included in the Saint Vrain district. 


On 


GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


G5 


James creek is the Central district. South of Left hand creek is the Gold Hill district, with the Sunshine district 
nearer the foot-hills, and at the head of this creek is the Ward district. Still south of this, between Four-mile creek 
and North Boulder, is the Sugar-loaf district, and south of Boulder creek Magnolia district, while at the head of 
Middle Boulder creek is Caribou or Grand Island district. , 

Geological.— The general geological structure of the district is simple and typical of the mining districts 
on the eastern slope of the Colorado range. Along the foot-hills immediately adjoining the plains is a series of 
so-called hog-backed ridges, formed by upturned Mesozoic strata resting on the Archaean core of the range. These 
upturned sedimentary beds form a fringing belt, of a width varying with their angle of dip, along the entire extent of 
the eastern foot-hills. Just south of Boulder their angle is almost vertical, and they form a prominent peak, rising 
to an elevation of over 8,000 feet, or 3,000 feet above the plains. The upper member of the sedimentary series, 
the Laramie or Lignitic group, contains valuable coal deposits, whose outcrops, by erosion at Boulder, have been 
moved out some distance on the plains. Besides coal, these beds furnish admirable building-stone and tlagging, 
and also fire-clay and lime. Of metallic minerals, however, they have as yet proved barren. The Archaean rocks 
immediately adjoining the plains have generally been found to contain but few valuable minerals, and it is not 
until the range has been penetrated for a distance of several miles that prominent deposits appear. 

In Boulder county the mines are found within 2 miles of the plains. The Archaean rocks of the Boulder district 
consist mainly of gneiss, intersected by veins of pegmatite (or coarse-grained secondary granite) varying in width 
from a few inches to 40 or 50 feet. In addition to these there are later eruptive rocks of Secondary age, occurring 
either in dikes or massive bodies, of whose extent and character only imperfect data are obtainable. The 
prevailing gneiss of the region is of a type of rock not uncommon in other mining regions; and for purposes of 
description the name “ granitegneiss” has been adopted for this, for the reason that it is largely a massive rock, 
in which the bedding is either indistinct or not at all visible. At times this gneiss is coarsely crystalline, at others 
fine-grained, in which case the proportions of hornblende and biotite are relatively greater and the rock assumes a 
darker color. Quartz is alway s prominent in it. In the coarse rock two feldspars are visible, an orthoclase feldspar, 
generally of a delicate pink tinge, and a white opaque feldspar, which is triclinic, and frequently shows the 
characteristic striation on the basal cleavage faces. In a specimen from the eastern base of Sugar-loaf, examined 
microscopically, plagioclase feldspar is largely predominant, and is of two varieties, one probably oligoclase, the 
other labradorite. Magnetite, apatite, and pale zircons are sparingly present. This granite-gneiss generally forms 
rounded hills with extensive debris slopes, and presents but few prominent or angular outcrops. 

The pegmatite veins, or gangues, as they are locally called, are mostly composed of white feldspar and quartz. 
Tarts of them are coarsely granular and contain some mica, others are like a fine-grained granite, and in still others 
these two textures are found bearing irregular relations to each other. Sometimes they are not more than a finger thick, 
crossing the rock in every direction without intersecting each other, and sometimes they consist entirely of quartz. 
Two of these veins have strongly marked characteristics, and have been traced for a number of miles through the 
district. The first, the Maxwell gangue, runs a little east of north from Four-mile creek to Left-hand creek,crossing 
the road to Sunshine, two miles from Boulder, and is said to carry pyrites and some tellurides. The Hoosier gangue, 
which is supposed to form the western limit of the telluride belt, is about 30 feet in width, and runs through Gold Hill 
in a direction east of north. A specimen examined in this belt is like fine-grained granite in appearance, though 
consisting chiefly of quartz and feldspar, with black metallic particles macroscopically visible. The microscope 
shows only quartz, orthoclase, microcline, the remnants of biotite and titauite, and apatite in small prisms. The 
quartz contains fluid inclusions and hair-like microlites of rutile. This carries silver ore and gray copper. The 
telluride belt includes the Magnolia, Sugar-loaf, Gold Hill, and part of the Central districts. In this belt eruptive 
rocks are very rare, but the pegmatite veins are extremely common. West of this region are enormous masses of 
eruptive rock, and tellurides are not found. 

In the Caribou district are rich silver ores carrying from 30 to 1,500 ounces of silver to the ton, and in the 
Ward district veius carrying free gold, with iron and copper pyrites, which have a general direction east and west, 
while the others are more nearly north and south. 

Of eruptive rocks, that which forms the Sugar-loaf, a conical hill between Four-mile and Boulder creeks, is a fine¬ 
grained porphyritic rock of grayish color, showing in the hand specimen small white feldspars, biotite, hornblende, 
and titanite, the latter,of ayellowcolor, being quite frequent. Under the microscope the rock shows some augite and 
a crystalline groundmass containing a little quartz, but it is made up chiefly of feldspar, in rounded particles, not 
sufficiently wed defined for their determination. A somewhat similar rock occurs on the north bank of Four-mile 
creek, which is more markedly porphyritic, its constituents being larger, and the large feldspar predominantly 
orthoclase. This rock is evidently a massive eruption of very considerable extent, as it apparently forms a much 
larger hill west of the Sugar-loaf and large outcrops up the north branch of Four-mile creek, nearer to the Ward 
district. In the saddle immediately east of the Sugar-loaf is a small dike of diabase, and about half a mile east is a 
larger one of the same rock, the former a dense black rock, in which only small plagioclase crystals can be 
distinguished, the other a granular mixture of augite, feldspar, and ore particles. Both are free from olivine. 
The former has a little globulitic glassy base, while the latter is entirely crystalline. 
vol 13--5 



66 


PRECIOUS METALS. 


At Jamestown (also known as Jimtown) occurs a normal quartz-diorite of rather light color, although i t contains 
considerable hornblende. Titanite is also abundant in this rock, and it forms a dike, running east and west, almost 
in the street of the town. The cliffs, over 500 feet in height near Jamestown, are formed of quartz-porphyry of a 
white color, which is partly due to alteration and partly to the absence of basic minerals. It is composed of pale 
llesk-colored ortkoclase, sometimes having crystals one inch in diameter, with quartz, which is not particularly 
prominent, and occasionally a bleached mica. The ground-mass is micro-crystallioe, and consists almost wholly of 
quartz, with a few small crystals of ortkoclase and plagioclase feldspar. By its appearance it should be an older 
rock than any of the others. It contains 07 per cent, of silica, and by assay no gold. 

A dike is found in the Ward district which contains pyrites, a 1 is supposed to be a continuation of one of 
those in the Sugar-loaf district; but as no specimens were obtained, its determination could not be made. Still 
another dike, called the Black Eagle, south of Sugar-loaf, is said to have been traced 16 miles in an east and west 
direction. 

Mines. —The mines of Boulder county are chiefly noted for the occurrence of telluride minerals, next to the 
native metals the richest and rarest ores that occur in nature. 

The telluride belt occupies the eastern part of the district, extending to within a short distance of the sedimentary 
beds on the east. Its western limit may be roughly defined by a line running from Jamestown west of Gold Hill and 
through the Sugar-loaf. It comprises, as already stated, the Magnolia, Sugar-loaf, Central, and Sunshine districts. 
West of these it is said that no tellurides have been found. In Caribou district, where the earliest discovery was 
made in 1869-’70, the ores are mainly argentiferous galena, and are generally quite rich. In the Ward district, at the 
head of Left-hand creek, the ores are largely pyritiferous, and contain, where decomposed, free gold, but are generally 
difficult of reduction. In the Saint Train, on the other hand, where comparatively small developments have been 
made, there are large veins rich in copper, but contain little silver. 

The district as a whole is characterized by exceptionally rich ores, in spite of which development has been very 
irregular and production uncertain. This is due in large part pvobably to the somewhat irregular manner of 
occurrence of the ores. The veins, which are popularly regarded as true fissure veins, and generally stand at a 
steep angle, are often of great width, but the rich ore, on the other hand, is concentrated in thin streaks and not very 
continuous bodies. If we confine the term true fissure vein to its narrowest limits, and apply it only to that form of 
vein which was once evidently a strong, deep-seated, open fissure that has been filled iu by vein matter and ore 
foreign and distinct from the country rock, there are probably no true fissure veins in this district. As far as 
known, the vein material is almost without exception an alteration of the country rock, which is impregnated with 
rich mineral. This impregnation has taken place either along the contact of a porphyry body with the country rock 
or in a pre-existing vein of pegmatite, or again along some fault or jointing plane in the country rock itself which 
has been favorable to the concentration and precipitation of metallic minerals from their solutions. The direction 
of the veins is in general between northeast and northwest, but in Ward district an east and west direction seems 
to prevail. Their plane, as already stated, stands at a high angle, approaching the vertical. 

Placers have been worked at various points in the narrow valleys which intersect the districts. Though rich, 
their superficial extent cannot be great, and no data have been gathered in regard to them. 

Minerals. —No exhaustive mineralogical study has yet been made of this interesting region. Among such 
rare deposits the temptation to discover new species is great, and it is necessary to accept with caution the statements 
as to their occurrence. In the list below the attempt has been made to give as complete as possible an enumeration 
of the unusual minerals occurring here under the following categories: I. Tellurides— a. Old species proved to 
occur, and cited by standard works on mineralogy; b. New species recognized by standard works on mineralogy; 
c. New species, probably good, but needing further investigation ; d. Mixtures described as species. II. Other 
minerals mentioned which have not been confirmed by publication or analyses. The occurrence of those marked with 
an asterisk is doubtful either as a species or in point of occurrence, and needs further investigation. 

I. Tellurides — a. Old species proved in Boulder county: 

Altaite (PbTe); anal, by Genth. (Cited by Dana and Naumann-Zirkel). 

Hessite (Ag./Te); anal, by Genth. 

Hessite, auriferous=petzite. Genth; not indep. sp. 

Sylvanite (AgTe- 2 +AuTe 2 ); anal, by Genth. Cited by D. & Z. 

Tellurite (Te0 2 ); anal, by Genth. Cited by D. & Z. 

Tellurium, native, Genth. Cited by D. & Z. 
b. New species recognized : 

Calaverite [M(AuTe) 2 +AgTe 2 ], sp. by Genth, from Calaveras co., Cal. Cited by D. & Z., sometimes 
regarded as a variety of sylvanite. 

Coloradoite (HgTe), sp. nov. by Genth. Cited by D. & Z., orig. from Boulder co. 

Schirmerite [3(Ag 2 Pb) S+2(Bi 3 S 3 )J, sp. nov. by Genth. Cited by D. Grotk and Z. A mineral of the 
same name by Endlick, from the same locality, is pronounced a mixture. Orig. from Boulder co. 


GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


67 


c. New species needing - further investigation : 

Ferro-tellurite (FeTe0 4 ), sp. nov. Gentb. Mentioned by Groth. Orig. from Boulder co. 

Magnolite (Hg 2 Te0 4 ), sp. nov. by Gentb. Orig. from Magnolia district; decomposition product of 
coloradoite mentioned by Groth. 
cl. Mixtures described as species : 

Henryite, Endlicb. Universally pronounced a mixture. 

Lionite, sp. nov. by Berdell. Considered impure tellurium by Dana (App. Ill, p. 119). 

Tellure-pyrite, J. A. Smith. Descr. by C. U. Sheppard; from description, probably a mixture. 
e. Menorite (Ni 2 Te 3 ), sp. nov. by Gentli. Orig. from California. No anal. Smith authority for Boulder co. 

II. Other minerals mentioned: 

* Amalgam. Authority, Smith. 

Argentite. Authority, Smith. 

' *Bismuth, native, sulphide, and carbonate. Smith. 

Copper, native, minute crystals. Smith. 

*Iodyrite. Endlicb. 

*Kobellite. Smith. Sp. not recognized in Dana. 

Mercury. Smith. 

*Pyrargyrite. Endlicb. 

Roscoelite. Sp. nov. Gentb. Boscoe believes it a mixture. 

Central district. —The most prominent mine in this district is the Golden Age, near Jamestown. It is on 
the contact of porphyry with the Archman, the former constituting the hanging wall. The vein is about 40 feet in 
width. The richest ore comes from a streak of white quartz from 1 to 2 feet thick on the foot wall, which is 
sometimes almost a mass of free gold. Pyrites prevail toward the hanging wall, but small rich concentrations of 
gold are also found at intervals. 

Gold Hill district.— This is in the telluride belt, and is traversed by the Hoosier gangue. Many of the 
telluride veins cross the Hoosier gangue, and are said to be richer in its neighborhood. The most prominent among 
these are Cold Spring and Goldsmith Maid. The Red Cloud is the oldest mine in the district, and is the one in which 
tellurides were first discovered in 1872. Its vein is 3J feet in width, and the ore was tellurides at the surface and 
auriferous pyrites in depth. The Slide, Melvina, and Prussian are also important deposits. The Emancipation is 
near the Sunshine district. All these are in the granite-gneiss, which here offers but few good exposures. The 
Washington Avenue mine, west of Gold Hill, carries galena, blende, and pyrites. 

Sunshine district.— This district comprises the easternmost development of the telluride belt. Its ores are 
generally of lower grade, free gold and tellurides occurring in the upper portion, passing into pyritiferous ores in 
depth. Prominent mines are the American, Grand View, Sunshine, Osceola, and Young America. 

Sugar loae district. —In this district the Yellow Pine mine is an enrichment of the Hoosier gangue of 
pegmatitic granite. Other prominent mines are Baile’s lode and the Emerson, both carrying telluride in granite- 
gneiss. 

Magnolia district.— This is at present the southern limit of the telluride line. Here, as well as in the 
neighborhood of Jamestown, the gueissic character of the country rock is very distinct, and the bedding planes are 
easily distinguishable. The prevailing strike seems to be in a northeasterly direction, which is also that of most 
of the veins of the telluride belt. The Senator Hill is one of the most promising mines of the district. In the 
Keystone and Mountain Lion, which are said to be on the same vein, a narrow deposit only from 0 to 7 inches in 
width, the new mineral coloradoite is found. 

Ward district. —Between Gold Hill and Ward the gneiss is much contorted and the bedding very plain, and 
bodies of eruptive rock, which were comparatively wanting in the telluride belt, are here frequent. The most 
important mines are the Niwot, Columbia, and Stoughton. The ores are sulphides of iron and copper, carrying- 
gold, and therefore, when undecomposed, difficult to reduce. 

Caribou or Grand Island district is situated at an elevation of nearly 10,000 feet above sea-level. Its 
most important mine is the Caribou, which was discovered in 1869, and has produced a very large amount of silver 
ore. This is a massive mixture of galena, chalcopyrite, and zincblende, which occurs in gneiss, but closely associated 
with diabase. Other important mines are the No Name (which is said to cross the Caribou and fault it), the Boulder 
County, and Native Silver. The ores of this district are essentially silver-bearing, but also carry some gold. 


68 


PRECIOUS METALS. 


Mine. 


CENTRAL DISTRICT. 
Golden Age (near Jamestown). 

Smuggler. 

COLD HILL DISTRICT. 

American. 

Cold Spring. 

MAGNOLIA DISTRICT. 

Keystone. 

Mountain Lion. 

WARD DISTRICT. 

Nelson. 

Niwot. 

SUGAR-LOAF DISTRICT. 


Country rock and vein. 


Ore and gangue. 


Foot wall cneiss; hanging wall porphyry. Vein vertical; strike, Free gold, with iron and copper pyrites and quartz. 
E. and W.; dip, 44°; 40 feet wide. 

Mica-schist. Strike, N. and S.; dip, 00° E. 


Granite-gneiss. Strike, NE.; dip, 84° SE. 


No specimens. From the gangue it is apparently line-grained 
granite, and a much-altered porphyry is near by. 


Gneiss. No specimens. Vein : dip, 65° ; 2 feet wide 
Gneiss. Vein: strike, NE.; dip, 65°; 2 feet wide 


Decomposed mica-schist. Strike, NE.; dip, 62°. 


Granite-gneiss hanging wall and porphyry foot wall. Strike, E. 
and W.: dip, 70° N. 


Tellurides and pyrites in siliceous gangue and altered country. 


Tellurides of gold, silver, and mercury, with free gold, sul¬ 
phide of iron, zinc, lead, and copper; ho specimens. 

Tellurides. Specimen, evidently from the side of the vein, is 
attrition material; clay, rounded pieces of quartz, with py¬ 
rites and tellurides. 

Tellurides in quartz gangue. No specimens. 

Iron oxide and free gold, with tellurides. Gangue: quartz and 
feldspar. 

Auriferous chalcopyrite and pyrite with free gold. Gangue: 
quartz and altered country. 

Massive pyrite and chalcopyrite cemented by quartz. 


Emerson. 

Yellow Pine. 

Baile’slode. 

GRAND ISLAND DISTRICT. 


Altered gneiss. 

Granite, with reddish feldspars and but little mica.. 

Coarse granite-gneiss with red feldspars, in which are veins of 
tine-grained hiotite-granite. 


The same rock impregnated with fine grains of pyrite and tel¬ 
lurides. 

Gray copper, azurite, malachite, and some unknown greenish 
mineral in a decomposed gneiss or granite. 

At the contact of granites is quartz with a little galena, pyrites, 
and black stains. 


Boulder County 

Caribou. 

Horsefall lode. - 
Native Silver .. 


Vein: strike, E. and W.; dip, 55° N 


Syenitic gneiss. Diabase occurs in the neighborhood. Vein: 
strike, E. and W.; dip, 14° N. (76° 1 ) 

Mica-schist. No specimen. Strike, E. and W.; dip, 85° N. 


A fine-grained hiotite-granite. Near the vein the biotite has dis¬ 
appeared. Vein: strike, E. and W.; dip, 5° N. (85°?) 


Galena, pyrite, and blende in quartz ; blende crystals covered by a 
layer of hematite. 

A massive mixture of galena, chalcopyrite, zincblende, and a 
mineral called “antimony ”. 

Chalcopyrite and pyrite with free gold, some galena and zinc- 
blende. 

Mixture of galena and sulphides. 


JEFFERSON COUNTY. 

This county includes the foot-liill region south of Boulder county as far as South Platte river and a narrow strip 
of the mountain region. Although mainly a mountain county, and surrounded by important miniug districts, it 
reports no product of the metallic minerals. On the other hand, its production of coal from Ralston creek, Golden, 
and Morrison, and of valuable fire-clays and building-stone all along the foot-hill region, is extremely important. 
From the basaltic mesas at Golden a number of interesting zeolitic minerals have been obtained by Mr. Cross, of the 
United States geological survey, among which are analcite, apophyllite, chabazite, laumontite, mesolite, natrolite, 
scolecite, stilbite, and thomsonite. Jet is also found in the Tertiary beds under the lava flows and bole. 

GILPIN COUNTY. 

This is the smallest county in the state, and consists of a triangular bit of mountain region, covering 180 square 
miles of surface, drained by the north fork of Clear creek and adjoining Jefferson couuty on the west. It is the 
oldest mining region in the state, the first gold being discovered here in Russell gulch in 1859, and is still the 
greatest gold producer. Its placer deposits, lying along the bottoms of deep ravines, are of limited extent, but 
they are extremely rich, and though most of them have been worked over several times, they still yield a certain 
amount of gold. 

This county is entirely in the Archaean formation, which consists mainly of gneiss, the prevailing type being 
structureless granite-gneiss, already described in the section on Boulder county. The gneiss is penetrated by 
various bodies of porphyry; but, owing to the peculiar readiness with which the rocks yield to atmospheric influences, 
few characteristic outcrops are found, so that the geological structure is not readily recognized on the surface. 
Here also the veins are mainly alterations of the country rock along certain planes, and rarely, if ever, show the 
character of a pre-existing open fissure filled by foreign material. In some cases the vein material seems to be a 
porphyry dike. Many of the veins have been traced to a very considerable depth, in some cases to over 1,000 feet, 
and it is claimed that some have been traced in length between 2,000 and 3,000 feet. The direction of the veins lies 
either between north and south and northeast and southwest, or within 10° of east and west. Among the more 
important veins the Gregory & Briggs, Bates, and a few others belong to the former, the Bobtail, Burroughs, 
Gunnell, and others belonging to the latter group. In all the dip is generally near the vertical. Faulting or 
displacement of the vein is rare, but where the vein material is porphyry it frequently contains inclosed fragments 
of gneissic country rock. In one mine rounded boulders of gneiss of considerable size have been found in the vein 
at a depth of about 700 feet from the surface, but whether their form is due to attrition of the two walls or to the 
rounding action of water and mineral solutions is not known. 







































GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


69 


The ores are mainly a mixture of pyrite and chalcopyrite, with less frequently galena and zincblende. carrying 
more or less gold. In the northern portion of the district, however, galena ores, with zincblende and pyrite, carrying 
silver, occur, but as a rule contain little or no gold ; and similar deposits almost surround the extremely circumscribed 
limits of the gold-bearing area, whose radius, taking Central City as a center, is only about 1J miles. In the gold 
veins the richer ore generally occurs in streaks that are not more than one foot wide, a compact line-grained 
mass of pyrite, copper pyrite being as a rule richer than the ordinary pyrite. The rest of the vein, which often 
attains a width of many feet, carries pyrites (irregularly disseminated through a more or less decomposed mass of 
country rock) either in the form of white clayey material or as a mixture of quartz and feldspar. Outside the 
narrow streaks of solid sulpliurets, the bulk of these ores, as they are extremely difficult to smelt, are generally 
treated by mill process, and the percentage of loss is generally much higher than in more completely oxidized ores, or 
those which are free from pyrites, averaging probably 40 per cent. The richer portions of the ore and concentrations 
of mill tailings are sent to the smelting works in the valley below. According to Mr. A. N. Eogers, of the Bobtail 
mine, who has had long experience in the underground workings of this district, the veins invariably follow the 
cleavage planes of the country rock, the planes crossiug the strata with a nearly vertical dip, while the stratification 
of the country rock has a dip to the eastward. He also states that the porphyry has its cleavage in common with the 
country rock where the cleavage does not invade the veins themselves, the joints or laminae taking the line of the 
veins and lying parallel with their walls. Hence he reasons that the porphyry is older than the veins, inasmuch 
as the cleavage is older and intersects the porphyry. These observations are of interest as giving a slight 
indication of the age of deposits in the Archaean, for which, as a rule, it is impossible to obtain any definite data. 

The mountain region, from 12 to 15 miles in width between the mining districts and the plains, mainly included in 
Jefferson county, which consists also of Archaean rocks, has hitherto proved relatively barren of valuable minerals. 
In this region the rocks are comparatively undecomposed and the bedding planes remarkably distinct, having a 
prevailing easterly dip. They are generally gneissic in character, with some granite, and, as a rule, are highly 
siliceous. 

Minerals. —Besides the ordinary sulphides of iron, copper, zinc, and lead, sulphides and arsenides of silver 
are found ; and among rarer minerals the occurrence of enargite (sulphide of copper and arsenic) iu massive crystals 
in the Powers mine, in Russell district, is noteworthy. From the Wood mine, in Leavenworth gulch, a small pocket 
of pitchblende or uraninite was obtained by Mr. Richard Pearce, who first noticed it in the refuse of the dump. 
Auriclialcite is reported by Dr. Gentk in connection with zinc minerals, cobellite by Dr. Loew, and melaconite by 
Dr. I*eters with copper minerals. 

The following minerals are reported from this county by J. Alden Smith and Dr. Endlich, but no analyses are 
given: Allopliane, azurite, calamine, chalcauthite, cerargyrite, copper (native), garnet, gold (in crystals), goslarite, 
greenockite, jarosite, lievrite, magnesite, magnetite, magnetic pyrite, marcasite, mispickel, molybdenite, selenium, 
siderite, smithsonite, sulphur (native), tourmaline, willemite, wolfenite, zincite, and a variety of uranium minerals. 

Mining districts.— The mining districts, like the county, are extremely small, and their limits not definitely 
known. The Gregory district includes the mines in the immediate vicinity of Black Hawk and Central, the most 
important being the Bobtail, which is the richest and largest producer, although worked on a length of only 
800 feet. On the Gregory lode claims have been located over a length of 4,500 feet, but actual explorations 
cover an extent much less than half of this. It is expected that these two lodes, together with the Bates (which 
lies to the northwest of the Gregory and nearly parallel to it), whose courses are convergent, will all unite to the 
southward in the Mammoth lode. Nevada district, which lies to the west of the Gregory, takes in the head of 
Nevada gulch, and includes the California, Kansas, Burroughs, and other lodes. The Russell district lies to the 
south of these, in Russell gulch. The number of mines is too great to admit of any special mention, but the 
following table gives the data furnished by specimens collected by the census experts: 


Mine. 

NEVADA DISTRICT. 
American Flag. 

California. 

Hidden Treasure. 

Jones. 

Kansas. 

Bennett's Kansas. 

Kent County. 

Lacrosse (Burroughs) — 
Pyrenees. 

Polk County.. 


Country rock and remarks. 


Ore and gangue. 

# 


Gneiss rich in biotite.... 

Granite-gneiss impregnated with pyrite. A dike of quartz-por¬ 
phyry 2 feet thick on the hanging wall. 

Same walls as in the California mine... 

Fine-grained granito. 

Biotite-gneiss ; fresh on foot wall, altei'ed on hanging wall. 

Light granite-gneiss. 

Gneiss. On the hanging wall dark blende concentrated iu the 
fissures. 

Fine-grained biotite-gneiss. 

Dark gneiss rich in biotite. 

Hanging wall fine dark mica-schist. 


Galena, copper, and iron pyrites, and some zincblende, cemented 
by quartz. 

Pyrite. chalcopyrite, zincblende, and galena, with siliceous 
cement; in some portions gray copper. 

Chalcopyrite and dark blende. Gangue: altered country rock. 

Dark blende, with pyrite, and some chalcopyrite. In one case 
t hese are deposited on both sides of a thin fragment of granite- 
gneiss. 

Fine-grained mixture of pyrite, chalcopyrite, and fahlerz. 

Fine-grained mixt ure of pyrite and chalcopyrite, with siliceous 
cement, associated with fragments of wall-rock. 

Pyrite, chalcopyrite, galena, and dark zincblende, with quartz 
I cement. 

Pyrite, with fragments of decomposed wall-rock. 

Massive galena, with chalcopyrite and pyrite; also fragments 
of wall-rock cemented by blende and pyrite. 

Chalcopyrite, with some pyrite cementing fragments of gneiss. 




































70 


PRECIOUS METALS. 


Mine. 


Country rock and remarks. 


NEVADA district —continued. 
Sayr-Burroughs. 

"West Flack. 

Forks. 

GREGORY DISTRICT. 
Bobtail. 


Cashier. 

Centennial tunnel. 

German. 

Minnie.. 


Smith. 

Wain. 

United Gregory 


RUSSELL DISTRICT. 
Haseltine. 


Powers. 

Silver Dollar. 
Wyandotte -- 


ENTERPRISE AND MOUNTAIN- 
HOUSE DISTRICT. 


Cyclops. 
Fannie . 
Toronto. 


ILLINOIS CENTRAL DISTRICT. 

Egyptian. 

IIAWKEYE DISTRICT. 

Hard Money.. 

EUREKA DISTRICT. 

Gunnell.. 

QUARTZ VALLEY DISTRICT. 

Boss.. 


Fine-grained gneiss.. 

Gneiss. 

Eeddish granite. 

Fine-grained compact granite-gneiss, partly schistose on the 
foot wall. 

Granite-gneiss impregnated with pyrite. 

Gneiss.. 

Gneiss. 

Felsite-porphyry impregnated with pyrite, and carrying frag¬ 
ments of Archasan rocks. 

Gneiss. 

Amphibolite foot wall. 

Apparently gneiss. 

Gneiss. 

Micaceous gneiss.. 

Gneiss. A porphyry dike occurs near the mine. 

Gneiss. Gangue: fine-grained white quartz-porphyry.i 

Gneiss..-.i 

Granite. Altered porphyry occurs at 70 feet distance. 

Gneiss. 

Altered gneiss. 

Altered gneiss. 

> 

Altered and stained gneiss. 


Ore and gangue. 


Fragments of wall-rock with a little pyrite, or massive pyrite 
with siliceous cement. 

Pyrite and chalcopyrite, with quartz. 

Coarse pegmatite impregnated with, galena, pyrite, and chalco¬ 
pyrite. 

Chalcopyrite, with some pyrite, cemented by quartz. 

Quartz and pyrite. 

Chalcopyrite and pyrite in altered country rock. 

Pyrite and chalcopyrite with quartz. 

Porphyry heavily impregnated with pyrite. 

iMassive mixture of pyrite, chalcopyrite, zincblende, and galena. 
I Gangue: altered country. 

Pyrite and chalcopyrite. Gangue : altered country. 


Mixture of pyrite and fluorite; galena and fahlerz occasionally 
present. 

Massive enargite, with pyrite and fluorite. 

Enargite, fahlerz, and pyrite. Gangue: feldspar and quartz. 
Pyrite. Gangue : quartz and feldspar. 


Mixture of galena, blende, chalcopyrite, and occasional ruby sil¬ 
ver. Gangue rock: white porphyry. 

Decomposed granite, in which cerussite and chlorides have been 
deposited. 

Pyrite, with copper and arsenical pyrites and zincblende. Gan gue: 
quartz and feldspar. 

Massive galena, with some cerussite and zincblende. Gangue: 
bleached and kaolinized country rock. 

Massive chalcopyrite and pyrite. Gangue: altered country rock. 


Cerussite; alteration products of galena, with stains of copper. 
Gangue: altered country rock. 


CLEAR CREEK COUNTY. 

Clear Creek county lies to the south of Gilpin, and is considerably larger than the latter, having an area of 460 
square miles. It extends from the western boundary of Jefferson county to the crest of the Colorado range, and 
is, next to Lake county, the largest producer of silver in the state. Its mines lie mainly among the steep rocky spurs 
between the various tributaries of the main Clear creek, but it includes also the Geneva district across the divide on 
the south, at the head of the Geneva creek, a tributary of the South Platte. Like Gilpin county, this county lies 
in the Archaean formation, the rocks being mainly gueissic, with subordinate development of granite. Porphyry 
dikes seem much more frequent than in Gilpin county, but this may be due in part to the steepness of the mountain 
slopes, on which the character of the country rock is more readily distinguished. The veins, like those of Gilpin 
county, seem to be mainly alterations of the country rock along a jointing or fault-plane, and are frequently in 
direct connection witty the porphyry dikes, which form either one of the walls or constitute the vein material itself. 
In some cases also the vein seems to be an impregnation of a pre-existing pegmatite vein in the gneiss. 

Minerals. —The ores of Clear Creek county are essentially silver-bearing, the silver being derived from 
argentiferous galena, and in part from fahlores. In the eastern or lower portion of the district, where the earliest 
developments were made, the ores are, however, mostly pyritiferous, and contain relatively little galena, hence yield 
both silver and gold. In the upper districts, around Georgetown, they are mainly silver-bearing. The rich ores 
are smelted directly, and are generally sent out of the district for this purpose. A very considerable proportion of 
the product is, however, concentration ore, which is generally an impregnation of the country rock at a greater or 
less distance from the main crevice. This impregnation seems to take place by preference on one side of the vein, 
and this is generally the foot wall. These ores are concentrated, as a rule, in Georgetown, and the concentrates are 
sold to smelters. A relatively small proportion of the oxidized portion of the deposits, especially those which are 
comparatively free from lead and zinc, are suitable for milling. There is no doubt that this district contains an 
unusually large proportion of valuable veins; but their development has been incommensurate with the intrinsic 
value of the deposits for various reasons, among which are pernicious systems of working and the abundant cases 






























































GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


71 


of litigation arising from the close vicinity of the veins to each other and their frequent crossings. A very large 
proportion of the more important mines were closed at the date of visit, and consequently the returns obtained by 
the expert are far from complete. Under these circumstances it were useless to attempt to form any generalizations 
on the direction or interdependence of the veins as a whole. 

Besides the ordinary metallic sulphurets, the following minerals are reported as occurring in the county: 

Anglesite, argentite, azurite, bornite, bournonite, calamine, caledonite, chrysocolla, fahlerz, garnet, minium, 
proustite, psilomelane, pyromorphite, silver (native), stephanite, sternbergite, stibnite, tennantite, tetrahedrite. 

The following table gives the character of ore and country rock of the mines from which specimens were 
obtained: 


Mine. 


BANNER DISTRICT. 


Country rock and remarks. 


Ore and gangue. 


First National 
Big Chief. 


Nathan 


Mica-gneiss; finely bedded on hanging wall; iron-stained and schis¬ 
tose on foot wall. 

Mica-gneiss, containing on the foot wall a number of small pink 
garnets. 

Gneiss.. 


Quartz, stained reddish and yellow by iron oxide. 

Pyrite, chaleopyrite, fahlerz, and chalcosite, with quartz matrix. 
Gangue: altered gneiss. 

Crumbling iron-stained mass with no recognizable minerals; 
probably altered country rock. 


CASCADE DISTRICT. 


Muscovite. 

CORRAL AND TRAIL RUN DIS¬ 
TRICT. 


Hanging wall granite-gneiss; foot wall decomposed gneiss and 
felsite-porphyry. 


Stained breccia-like mass, with no distinct metallic minerals 
visible. 


Donaldson 


Brooklyn. 

GENEVA DISTRICT. 
Baltic. 

GRIFFITH DISTRICT. 


Hanging wall iron-stained gneiss; foot wall grayish compact 
felsite. 

Gneiss.. 

No specimen. 


Pyrite in quartz; smelting ore contains fahlerz; pyrite 
'thoroughly decomposed constitutes free-gold ore. Gangue: 
altered gneiss. 

Pyrite and chaleopyrite with fahlerz. Gangue: quartz and feld¬ 
spar. 


Pyrite, chaleopyrite, blende, fahlerz, and a little galena in siliceous 
"gangue; occasional pink calcite crystals. 


Burleigh. 

Consolidated Hercules 

Diamond.. 

Dunderberg.. 

Equator. 

Junction.. 

Colorado Central.. 


Gneiss, passing on one side into granite; on the other, into schists 


Porphyry and gneiss (a) 


Chiefly massive galena and chaleopyrite. 


Chaleopyrite and argentiferous galena. 


IDAHO DISTRICT. 


Champion 


Altered gneiss 


Gem 


Indistinctly bedded gneiss 


Idaho tunnel. 

Victor. 

IOWA DISTRICT. 


Hanging wall mainly white orthoclase ; foot wall gneiss 
Gneiss indistinctly bedded. 


Chaleopyrite and blende. Milling ore: altered country rock im¬ 
pregnated with particles of pyrite. 

Arsenical fahlerz with azurite and malachite. Gangue: altered 
country rock. 

Galena, zincblende, and pyrite deposited on hanging wall rock. 

Zincblende, pyrite, etc., altered in high grade ore to a stained 
decomposed mass. Gangue: altered country rock. 


Mackey. 

MONTANA DISTRICT. 

Free American. 

Murray. 

Joe Reynolds. 

MORRIS DISTRICT. 
Albro. 

Alexander. 

Eagle. 

SEATON DISTRICT. 

Tropic. 

SPANISH BAR DISTRICT. 
Fairmount-Shafter. 

Freeland. 


Hukill. 

Mayflower 


Gneiss. 

No specimen. 

White granite whose mica is altered to a light greenish substance 
Foot wall mica-gneiss; hanging wall pegmatite vein. 

Gneiss. 

Gneiss. 

Gneiss. 

Gneiss impregnated on foot wall with pyrites. i 


Gneiss impregnated with pyrites more abundantly on the foot 
wall. 

Gneiss varying in depth from a hornblendic variety to a feld- 
spathic. 

Much decomposed gneiss.- • 

Schistose gneiss of varying character. 


Ore and gangue specimens both granite-gneiss, the gangue 
specimen having more visible pyrite than the pay ore. 


Galena, pyrite, and barite. 

Galena, pyrite, and chaleopyrite. Gangue: altered country rock. 
Galena. Gangue: quartz and feldspar. 


Pyrite, chaleopyrite with some fahlerz. Gangue: quartz and 
'feldspar. 

Galena, pyrite, chaleopyrite, and possibly fahlerz. Gangue: 
quartz and feldspar. 

Seems to be mainly country rock impregnated with chaleopyrite 
and other minerals invisible to the eye. 


Brilliant mass of zincblende, with galena, fahlerz, and pyrite; 
concentration ore wall-rock more or less impregnated with these 
minerals and carrying calcite. 


Galena, pyrite, and pyrolusite. Gangue: feldspar in large in¬ 
dividual's. 

Fine-grained mixture of pyrite and chaleopyrite; relative rich¬ 
ness depending on proportion of latter. Gangue: altered country 
rock. 

Pyrite and bornite in siliceous gangue. 

Pyrite and galena, with some fahlerz and zincblende either mas¬ 
sive or mixed with siliceous gangue. Gangue: altered country 
rock. 


a Porphyry assays 0.033 to 0.083 ounce of silver per ton, with a trace of gold. 
































































72 


PRECIOUS METALS. 


Mine. 


UPPER UNIOX DISTRICT. 

Fred Rogers. 

Keith. 

Pioneer. 

VIRGINIA DISTRICT. 
Lake. 

Specie Payment. 

White Cloud. 

YORK DISTRICT. 
Clifford. 


1 • 

) Gneiss 


Country rock and remarks. 


Ore and gangue. 


Chiefly massive chalcopyrite. 


Gneiss. 

Gneiss.i. 

Gneiss on hanging wall 


Massive galena, chalcopyrite, and pyrite, with a little fahlerz. 
Gangue: altered country rock. 

Rich ore, pyrite in quartz; second-class ore, gneiss impregnated 
with pyrites. 

Pyrite with a little galena in quartz; low-grade ore, gneiss im¬ 
pregnated with pyrites. 


Gneiss. Slickensides occur 


Galena and zinchlende. Gangue: altered country rock. 


SUMMIT COUNTY. 

By the recent cession of the lands of the Ute reservation a large area of the mesa region of the Colorado plateau 
country between the White and Grand rivers, extending as far west as the boundary of Utah, has been added 
to what was originally a small mountain county. This new region, with the exception of the White River plateau, 
at the head of the White river, in which Palieozoic rocks, cut through and partially covered by basalts, are exposed, 
is mainly covered by Tertiary beds, and offers little prospect of metallic wealth. 

As originally constituted, the eastern end of Summit county adjoins Clear Creek and Park counties, the crest 
of the Colorado range separating it from the former, and the cross range connecting this with the Mosquito range 
and dividing the two parks from the latter, and includes a portion of the Park range, consisting of the northern 
end of the Mosquito range and the Gore mountains, together with the valleys of the Blue river on the east of these 
mountains, and of Eagle river on the west. 

The high mountain portion of the county is mainly composed of Archman rocks, but along the valley of the Blue 
there are fragmentary beds of Mesozoic and Palaeozoic rocks which have escaped erosion, relics of a former connection 
of the Mesozoic seas which filled the South and Middle parks. These rest on the Archaean of the Park range, and 
are repeated on its west side, the Park range probably having been lifted up by the great fault movement which is 
so well defined in the Mosquito range. Along the upper portion of Eagle river there are Palaeozoic beds dipping 
north and resting on the Archaean of the northern end of the Sawatch, which, as one goes westward down the stream, 
gradually pass under the succeeding higher Mesozoic beds, and are finally lost under the Tertiary of the lower Grand 
and White rivers. Associated with the lower beds is a very considerable development of Secondary eruptive rocks, 
which are very inadequately represented on the existing geological maps of this region. 

The lofty mountain crests which bound the county on the east have hitherto been a serious barrier to the 
development of its ores, which, though frequently occurring in large masses, are on the average of low grade, and 
canuot support heavy freight or reduction charges. The recent advent into the valley of the Blue river at Frisco 
of the Denver and Rio Grande road promises to ameliorate this condition of things to a limited extent ; but its 
circuitous course, which necessitates the carrying of freight from here to Denver over five times the actual distance 
in a straight line, still involves relatively high freight charges on supplies and ore. 

I 11 this county there is a marked connection between the prevalence of eruptive rocks of Secondary or Mesozoic 
age and the richness and magnitude of the ore deposits. These are not only found in the Archaean and Palaeozoic 
systems, but also extend up as high as the Trias. As yet none of value are known to occur in the Jurassic or 
Cretaceous formations. 

Mining districts.— The oldest mining districts are those in the neighborhood of Montezuma and Peru, near 
the head of Little Snake river, the east fork of the Blue, their veins belonging to the same mineral belt as those 
of Georgetown, in Clear Creek county, and of Geneva gulch and Hall valley, in Park county, from which they are 
respectively separated only by the intervening curving crest of the Colorado range. The deposits occur in the 
Archman rocks, and consist mainly of argentiferous galena and sulphurets. Several presumably valuable mines 
have been developed in the district, and small smelting works have been erected, with the usual want of success 
attendant on small capital and a limited supply of ore. No report was furnished from this district. 

Numerous ore bodies have been found at the head of the Blue river, where the Palieozoic and Triassic formations 
have beeu extensively traversed by intrusive sheets of Secondary eruptive rocks. These eruptions have undoubtedly 
caused considerable local metamorphism of the sedimentary beds, which have further been extensively dislocated 
by a complicated system of faults, so that, without a careful study in the field, it is impossible to definitely determine 
the geological horizon of any individual deposit. The principal developments have taken place near Breckenridge. 
on the northwestern slopes of mounts Hamilton and Guyot. 

Reports are at hand from the Helen mine, in the Bevau district, in French gulch, whose ore body is an 
impregnation of quartzite, called a vein, striking NNE. and dipping 60° to the southward, and some 45 feet in 

width. The ore i$ free gold, with some silver in a quartzite, iron-stained by the leaching out of the pyrites which it 
originally contained. 
























GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


73 


In the McKay district the Naperville mine lias a deposit of argentiferous galena and carbonates occurring 
between an overlying porphyry and an unreported sedimentary bed below. 

The Monte Cristo mine, on the slope of Quandary peak, west of the upper valley of the Blue, is a deposit of 
low-grade galena, with some zincblende impregnating the Cambrian quartzite. This deposit is exceptionally 
favorably situated for mining, the quartzite bed in which it occurs dipping eastward at the same angle as the 
spur of the mountain, and the overlying white limestone and succeeding rocks above having been eroded off so 
that it forms the actual surface of the hill and can be quarried out. In spite of its low tenor in silver, said to 
average 15 ounces to the ton, it seems that under proper management the mine ought to be made to pay. Veins 
have been discovered at many points iu the Archaean rocks that form the sharp crest of the Mosquito range, often 
in the most inaccessible localities; but during the census year, so far as could be discovered, none were in the 
condition of producing mines. 

Ten-mile district, between the heads of Ten-mile creek, a fork of the Blue river, and of Eagle river, is at present 
the most important mining region of the county. The ores occur mainly in the Upper Carboniferous limestones 
and in the sandstone beds immediately above them. These lie at the western foot of the Archaean mass which forms 
the sharp, jagged crest of the Mosquito range, and which has been lifted up by the movement of the great Mosquito 
fault. An area here of some 10 miles square has been the scene of most wonderful eruptive activity during or at 
the close of the Mesozoic epoch. In number and size the intrusive bodies of porphyry and porphyrite which occur 
iu these sedimentary formations, either as iuterbedded sheets, as dikes, or as intermediate irregularly transverse 
bodies, exceed even those of the neighboring region of Leadville. Betweeu these two districts, but nearer that of 
Ten-mile, occurs a Tertiary eruptive mass of the rather uncommon rock nevadite, or crystalline rhyolite. Although 
but a portion of the probable ore-bearing area has yet been prospected, the quantity of metallic minerals found here 
is remarkable. Unfortunately for the prosperity of the district their quality is not so satisfactory, as they mostly 
run very low iu silver and are extremely refractory, consisting mainly of pyrites, with a very considerable admixture 
of zincblende. The ore deposits mostly occur in the thin beds of limestone, which are prevalent in this formation, 
at or near their contact with an overlying micaceous sandstone. Less frequently they are found in actual contact 
with an intrusive bed of porphyry, and at other times impregnating a dike of porphyry which traverses the 
sedimentary formations. 

The most important and the typical mine of the district is the Robinson. Its ore is an argentiferous galena 
of exceptionally high grade, associated with pyrites and some zincblende. It occurs at or near the surface of a bed 
of bluish-gray limestone, overlaid by a white micaceous limestone, dipping northward at an angle of about 17°. 
The ore seems to be an actual replacement of the country rock. The upper layer, locally called “ white iron”, 
which is a mixture of fine-grained crumbling pyrites with white mica, nearly free from galena, seems to be a 
replacement of a portion of the overlying sandstone, and is practically worthless. Below this the ore consists 
of a varying mixture of galena and pyrites, extending at irregular depths into the limestone, and in the larger 
bodies occupying nearly its whole thickness. The ore chute, whose maximum width is 100 feet, has been traced 
over a linear extent of 1,000 feet, following the general direction of the dip. A line of fracture, probably a 
fault-plane, may be observed in the roof following the line of the ore body, i. e., a vertical plane at right angles 
to the line of strike. It seems probable that this fault-plane furnished the channel through which the ore solutions 
reached the limestone, inasmuch as pyrites extend apparently into the fissure as far as it has been opened, and in 
the portions of the limestone adjoining there is no mineral matter at its contact with the overlying sandstone 
at a little distance from the ore body. Small bodies of mineral have also been found in the limestone along the 
line of several minor fault-planes, which are also at right angles to the line of strike, and whose displacement 
amounts at most to a few feet. The Wheel of Fortune, on the summit of Sheep mountain, at the foot of which the 
Robinson mine stands, has an extremely rich body of silver ore in the same or an adjacent limestone stratum and 
adjoining an irregular transverse body of white pdrphyry. 

On Elk mountain ore occurs over a very large area in a thin bed of limestone at a higher horizon than that of the 
Robinson. This ore is a similar mixture of pyrites and galena, oxidized near the surface, and sometimes to considerable 
depths along certain lines, with unaltered sulphurets on either side. This almost continuous body has been developed 
by the adjoining claims of the White Quail, Aftermath, Milo, Badger, Raven, Eagle, and Colonel Sellers to an extent 
of over 2,000 feet along the strike and 700 to 800 feet on the dip. While a great portion of this immense mass is 
too poor iu silver to pay for working, as an instance of widely extended ore deposition it is certainly remarkable. 
Where the same bed crosses the north end of Sheep mountain, a mile or two to the eastward, beyond an intervening 
gulch, similar great bodies of pyritiferous ores, with more or less argentiferous galena, are found in the Snowbank, 
Nettie B., Triangle, and other mines. 

Ore is found following the limestone horizons at higher levels and extending probably up into the Triassic 
formation. In one portion of the district, called Copper mountain, copper minerals are associated to some extent 
with the irou pyrites. 

The Pride of the West, on Jacque mountain, is a type of the deposits which follow a narrow dike of porphyry. 
Here the vein mass, which is from 6 to 50 feet in thickness, crosses the formation diagonally and stands 
nearly vertical. It is an iron-stained quartzose mass, through which run seams or veins of barite parallel with the 


74 


PRECIOUS METALS. 


walls, one being particularly persistent, and in connection with which the richest mineral is found. Where the 
siliceous gangue material is sufficiently unaltered it is found to be a decomposed quartz-porphyry. Another 
example of the type is the Little Chicago, which follows a dike of decomposed porphyry. This vein or dike yields 
an abundant supply of water, which is milky, from suspended particles of kaolin. Small jets of water from the 
adjoining rock also deposit hydrated oxide of iron, but the bodies of mineral as yet developed have been small 
and at widely separated intervals. 

On Eagle river, in the neighborhood of Eed Cliff, deposits of argentiferous galena and cerussite, associated 
with iron oxides, are also found in limestone, sometimes between it and an overlying white porphyry, and again 
with a limestone hanging wall and a quartzite foot wall. These limestone beds belong to the Palreozoic system, 
and are probably Carboniferous in age; but whether, like those of Ten-mile, they are in the upper portion of the 
Carboniferous, or, like those of Leadville, in the lower, is not known, nor is it of any practical importance. They 
are said to be very much broken and faulted. This district, as well as that of Ten-mile, is now reached by the 
Denver and Rio Grande railroad, and its ores are treated at Leadville or by some of the smelters on the plains. 

PARK COUNTY. 

Park county embraces the broad mountain valley of the South park, its boundary running along the crest of the 
Mosquito range on the west, and of the irregular chain which separates it from the Middle park on the northwest. 
It includes also, on the northeast, a portion of the Colorado range lying to the south of Clear Creek and to the 
west of Jefferson county. The valley plains are covered by sedimentary deposits of Mesozoic age, which, with 
underlying and conformable Palaeozoic formations, slope up to the crest of the Mosquito range on the west, but are cut 
off' abruptly against the Archaean on the east, probably by a fault. The coal beds of the Upper Cretaceous are thus 
included in this area, and have been extensively developed in the neighborhood of Como. Near Hamilton there are 
deposits of hematite iron ore, whose exact geological horizon is not known, and which have been but irregularly 
developed. Besides the less precious minerals, there are salt springs in the southern portiou of the park, from which 
at one time rock-salt was obtained, and which probably originated in deposits of this mineral in the Triassic 
rocks. There are also indications of copper in the sandstones of the Trias, in the form, usual in these strata, of 
impregnations of carbonate of copper accompanying plant remains. As yet none have been discovered of economic 
value. Minerals carrying the precious metals have thus far been developed only in the Palaeozoic formations, with 
their accompanying porphyries of Mesozoic age, and in the underlying Archaean. 

In the northeastern corner of the county are the Hall Valley and the Geneva districts, whose deposits properly 
form part of the Clear Creek belt of silver-bearing ores and occur in the same gneissic formation. The Whale 
lode, in the latter district, is one of the most characteristic. The country rock is here a fine-grained gneiss, with a 
general strike of north and south and a steep dip to the west. It is intersected by numerous veins of pegmatite 
composed largely of feldspar. The lode itself runs northeast and southwest, dipping to the northwest at an angle 
of 65°, and is a thin vein, consisting mostly of barite, carrying also fluorite and quartz, with irregular bunches of 
galena and gray copper, and often separated from the adjoining portions of the lode by a clay gouge. This vein 
varies from an inch to 3 feet in thickness. The crevice of the lode is between 5 and 10 feet in width, and outside 
the above-mentioned vein consists of altered gneiss, more or less impregnated with pyrite, galena, zincblende, 
and a decomposition product. The pyrite is said to be confined to the decomposed wall-rock, and seldom occurs in 
the vein proper. There are numerous other veins iu the vicinity of this lode which are also characterized by the 
occurrence of barite as gangue material. The Treasure Vault is said to have produced bismuth-silver ore. 

The principal mineral developments of the county have taken place along the eastern slopes of the Mosquito 
range, and have been mainly derived from Palaeozoic rocks, since, although numerous small deposits of gold and 
silver have been found iu the underlying Archaean, which is exposed near the crest of the range and in the deeper 
canons, and many interesting minerals have been obtained from them, no ore deposits of considerable value have 
yet been found in this formation. 

The Palaeozoic system here consists of the following series, commencing at the bottom: 


Feet. 

Cambrian quartzite. 200 

Silurian or White limestone. 200 

Lower Carboniferous or Blue limestone. 200 

Middle Carboniferous or Weber grits. 2,000 to 2,500 

Upper Carboniferous, consisting of limestones, sandstones, and conglomerates. 1,000 to 1,500 


These formations, as well as the underlying Archaean, have been traversed by eruptive rocks of Secondary 
age, mainly quartz-porphyries and porphyrites, which, in the Archaean, occur generally in the form of irregular dikes, 
but in the Palaeozoic system are mainly spread out in intrusive sheets between the beds. There is a marked connection 
between the prevalence of these eruptive masses and the development of mineral deposits. Indeed, in many cases 
here, as in the Leadville region, it is evident that the ore bodies are a concentration of the metallic minerals originally 
disseminated through the masses of these bodies and now deposited along their plane of contact with the sedimentary 
beds, and extending more or less into the mass of the latter. The type of these deposits may befound in mounts Lincoln 
and Bross, where most valuable and extensive ore bodies have been developed in the Moose, Russia, Hiawatha, and 







GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


r? ** 

other mines, which enjoy the further distinction of being the most elevated mines in the country, their altitude 
varying from 13,000 to 14,000 feet. The ores are mainly argentiferous galena and its products of decomposition, 
carbouate and sulphate of lead and chloride of silver. Barite is a frequent gangue material in the richest portion of 
the deposit. Pyrite also occurs with the ore, but is generally decomposed and changed to a hydrated oxide, 
associated with more or less oxide of manganese. These give to the mass of the ore, which frequently contains 
considerable mechanical admixture of clay, a red or yellow, or, where manganese predominates, a black color. The 
deposits occur in irregular bodies, often of great size, in the blue limestone, and generally near its upper surface. This 
blue limestone now forms the surface of the spurs of the mountain, sloping east at an angle of from 10° to 15°, but was 
originally covered by a sheet of quartz-porphyry, portions of which still remain on the highest parts of the peak. 
This quartz-porphyry, to which the local name of Lincoln porphyry has been given, is of a type so widespread 
throughout Colorado, and seems to be so intimately connected with the rich mineral deposits, that it is worthy of 
a detailed description. It is so thoroughly crystalline that it is often mistaken for granite. Its most striking, 
although not absolutely essential characteristic, is the occurrence of large porphyritic crystals of orthoclase of rather 
glassy appearance, with extremely well-defined faces, either in single crystals or Carlsbad twins, in size from a half 
inch to 2 inches in length. The ground mass is a crystalline mixture of two feldspars, in which plagioclase sometimes 
predominates, with mica or hornblende generally somewhat decomposed, and frequently a large amount of free 
quartz in double-pointed hexagonal pyramids, which often have the appearance of rounded grains. The quartz 
often has a pink tinge. The rock itself, taken comparatively fresh, is of greenish-gray color, but often bleached 
by decomposition or weathering. As to the age of the porphyry in this region, it can only be said that it is later 
than the Trias; but what is apparently the same rock is found in the Gunnison region, and between the Forth and 
Middle parks, breaking through the Cretaceous strata. It is, however, distinctly older than, and of a different 
character from, the Tertiary eruptive rocks. 

The Dolly Varden mine of Mount Bross is a similar deposit of slightly different type. Its ore, which is 
mineralogically similar, occurs in the mass of the limestone in close proximity to a vertical dike of white 
quartz porphyry. The dolomitic limestone in which it occurs is the same as that in which the previously described 
deposits are found; and the ore has been traced to a vertical depth of over 100 feet, and in bodies extending from 
40 to 50 feet on one side of the dike in the mass of the limestone. On Loveland hill, a spur next south of mounts 
Bross and Lincoln, are numerous deposits in the same blue dolomitic limestone, the best known of which is the 
Fanny Barrett, whose ore body stands vertically or at right angles to the stratification planes, and is probably 
deposited along a cross fissure or jointing plane. 

In Buckskin gulch, between these two mountain masses, is the oldest mine of the district, the Phillips, which 
is an immense mass of auriferous pyrites, also carrying some silver, deposited in the beds of the Cambrian quartzite 
near a dike of quartz-porphyry. The Criterion mine, on the north wall of the gulch, is also in the Cambrian 
quartzite—an immense body of thoroughly oxidized material, whose original character cannot be determined, but 
which was probably a varying mixture of galena and pyrites, carrying both silver and gold. A porphyrite dike 
occurs near by. Colorado Springs mine, in the Bed amphitheater on the southwest face of Mount Bross, is a rich 
deposit of galena along the bedding-planes of the white limestone. Here both diorite and quartz-porphyry are 
found traversing the sedimentary beds. The Sweet Home mine, near this on the cliff'face, in the underlying Arclnean, 
is principally interesting from the minerals which it lias produced—combinations of silver with arsenic and antimony. 
From the Tanner Boy, also in the Arcliman, on the opposite side of the gulch, beautiful rhombic crystals of 
rhodochrosite are obtained. 

In Mosquito gulch, the Orphan Boy, once an important mine, is in quartzite underlying the limestone 
bed. The London mine, on London mountain, at the head of Mosquito gulch, has developed two strong veins 
of sulphurets, carrying both gold and silver, the one with a gangue of quartz, the other of calcite, which occur 
either in the Blue or White limestone in connection with an intrusive bed of White porphyry. These veins stand in 
an almost vertical position, as the beds in which they occur are turned up at a steep angle against the London 
fault, which crosses the formation diagonally, and by whose movement the Archaean rocks, which form the eastern 
half of London mountain, are brought up into juxtaposition with the Silurian and Carboniferous beds on its western 
point. 

Southward the masses of intrusive porphyry diminish in extent, as do also the number of developed mineral 
deposits. Between Horseshoe and Sacramento gulches rich bodies of galena and carbonate ore, carrying silver, have 
been developed in the Sacramento mine, also in the Blue limestone, to the east, of the London fault, from whose 
surface the original covering of quartz porphyry has been denuded. On the west of the London fault the 
Peerless and Badger mines, the former at the very crest of the range, find their ore in the same limestone which 
here was cbvered by the White or Leadville porphyry. 

Placer deposits. —The mountain masses bordering the South park on the north and west have, owing to 
the great elevation, been exceptionally exposed to glacial action. An enormous amount of detrital material has in 
consequence been accumulated in the valleys radiating out from them, which, when rearranged and concentrated, 
forms valuable placer deposits. The first placer gold was discovered in Tarryall creek in the fall of 1859, and placer 
mining has been carried on since that time with more or less vigor in the valleys of the Tarryall and of the Platte. 


76 


PRECIOUS METALS. 


Near the town of Fairplay the banks of the Platte expose a thickness of over 50 feet of gravel, which has been 
extensively worked over by sluice mining, but is now abandoned. At present, active work is confined to the valley 
of the Platte opposite Alma, where hydraulic working is carried on and a gravel bed of over GO feet in thickness 
on the east bank of the creek is being developed. Two important conditions for hydraulic mining on a large scale 
are present in the county: first, an enormous amount of gravel, and second, an abundance of water. It only remains 
to be practically proved whether these accumulations of gravel are sufficiently rich to pay for working. 

LAKE COUNTY. 

Lake county is of small area, having only 450 square miles of surface, and occupying only about 20 miles of the 
upper valley of the Arkansas, its boundary following the crest of the bordering ranges. Since the discovery of the 
Leadville mines it has become second only to Arapahoe county in population, and furnishes three-fourths of the precious- 
metal product of the state. Its western boundary is the Sawatch range, which is an Archaean mass in which granite 
predominates over gneiss, and which abounds in dikes of porphyry. The western slopes of Mosquito range on the 
east, and the hills on the north which form the water-shed between the Arkansas and Grand rivers, have a basis 
of Archaean granite and gneiss, more or less covered by remnants of the Palaeozoic formations, already described in 
Park county, which have escaped erosion; and their lower position relative to corresponding beds on the eastern side 
of the Mosquito range is due in part to faulting and in part to flexure of the beds. Within these Palaeozoic 
formations there is an enormous development of eruptive rocks, partly occurring as irregular dikes, but in the main as 
immense intrusive sheets, following the bedding-planes of the sedimentary rocks. Glacial erosion here, as in other 
elevated districts, has played an important part in the carving of the present mountain outlines, and in the flood 
period following the first cold maximum of the Glacial epoch a lake was formed, which occupied the head of the 
Arkansas vallej', and was probably almost entirely included within the present boundaries of the county. The 
stratified gravel and sand beds which were deposited at the bottom of this lake now form terrace-like ridges bordering 
the present alluvial bottom of the Arkansas river. Whether the gold contents of these gravel beds, like those of 
California which may have had a similar origin, will be found to be, in any portion of them, sufficiently concentrated 
to be worked at a profit is a question which no steps have yet been taken to solve. The gravels resulting from the 
carving by erosion of the later-formed gulches have, however, been found to contain paying quantities of gold; and 
it was to the exceptional richness of those of California gulch, discovered in the spring of 1860, that the development 
of the enormous silver wealth of the Leadville region is indirectly due. Of late years the prominence given to silver 
mining has diverted attention from the gravel deposits, and their development has been practically stopped. It is 
probable, however, that a profitable field for hydraulic mining will be found in this county. 

The mineral product of the county is mainly confined to the California ruining district or the mines immediately 
adjoining Leadville, those of the outlying districts furnishing but a small fraction of the aggregate product. The 
ores are mainly argentiferous galena associated with zincblende, and, exceptionally, a little copper. They are 
essentially smelting ores, and their value is greatly enhanced by the fact that thus far they have been found in an 
oxidized condition, the lead occurring as carbonate, the silver as chloride, in a clayey or siliceous mass of hydrated 
oxides of iron and manganese. Here, even to a greater degree than in Park county, the main body of the ore is 
confined to the horizon of the Blue or Lower Carboniferous limestone, which is here invariably covered by an 
intrusive sheet of White or Leadville porphyry. The ore was at first supposed to be confined to the immediate 
contact of the limestone with the porphyry; but as developments have proceeded it has also been found to extend 
into the body of limestone sometimes to a depth of over 100 feet from its upper surface, and in such cases in large 
but very irregular deposits, as is characteristic of ore masses occurring in this rock. 

Less important ore bodies, generally carrying gold rather than silver, are fouud at other horizons, either 
along bedding-planes or in gash veins crossing the stratification. Such are the Colorado Prince and Miner Boy, 
in the Cambrian or lower quartzite, and the Green Mountain, Tiger, and Ontario, in the Weber grits, or Middle 
Carboniferous. The first mine opened in the district, and the one which has produced the largest amount of gold, 
is the Printer Boy, which is a deposit of free gold with carbonate of lead and galena, passing in depth into auriferous 
copper and irou pyrites, which occurs in a body of quartz-porphyry along a vertical plane or pair of planes 
nearly parallel, either as cross-joints or fault-planes. The gangue material is simply a white clayey mass resulting 
from the decomposition of the porphyry itself, and, although at times exceptionally rich, the ore seldom shows any 
visible metallic minerals. The Palieozoic formations and accompanying intrusive beds of porphyry have been 
compressed into gentle folds and broken by a series of faults having a general north and south direction whose 
movement of uplift is as a rule to the east. The prevailing eruptive rock is the White or Leadville porphyry, which 
generally occurs above the Blue limestone, but is also in places found below it and at other horizons. Besides these 
there are other intrusive sheets of different varieties of quartz-porphyry, generally of extremely local development. 
Along the western end or lower portion of the spurs of the Mosquito range on which the mines are situated the actual 
surface of the ground is very largely buried to a depth of 100 feet or more beneath an accumulation of rearranged 
glacial or moraine material, locally called wash. The extremely complicated conditions resulting from this state of 
things reuders it impracticable within the limits of the present sketch to give any detailed description of the geological 
structure of the district, and the reader is referred for this purpose to the memoir of the writer on “The Geology 
and Mining Industry of Leadville”. 


GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


77 


The most important groups of mines of the normal Leadville type, taken in the order of their development and 
of their relative distance from the valley, are as follows : (1.) Those of Fryer hill, which is the western extremity of a 
spur adjoining Evans gulch on the south, including the Chrysolite, Little Pittsburg, Little Chief, Amie, Climax, 
Duukin, Matchless, and Lee mines. In these mines the ore bodies, which reach a maximum thickness of 90 feet, lie in 
an approximately horizontal position, and are included between two sheets of White porphyry. In some cases these 
ore bodies are split up by the porphyry into two or more distinct bodies. They are distinguished from the deposits 
in other portions of the district by the almost entire absence of the original limestone, of which they are a 
replacement. (2.) The mines of Carbonate hill, which adjoins California gulch on the north, include the Carbonate, 
Yankee Doodle, Crescent, Catalpa, Evening Star, Morning Star, Henrietta, iEtna, and Pendery. Of these the 
seven first-named follow the contact of the limestone and the overlying porphyry on its dip into the hill at an angle 
of from 15 to 25 degrees, and are east of Carbonate fault, which runs across the face of the hill, while the last two 
find the limestone at a lower level on the west side of the fault. (3.) To the west of Carbonate hill a second shoulder 
of the spur is Iron hill, which has been elevated to its relatively higher position by the movement of the Iron fault, 
which, like that of Carbonate hill, runs along its western base. Here the principal mines are those belonging to 
the Iron Silver Mining Company, which with the Smuggler, and, south of California gulch, the Kock and Dome, 
find their ore at or near the surface of the easterly dipping limestone, while the ore of the Silver Wave and Silver 
Cord, also on Iron hill, and of the La Plata, in California gulch, is mainly found in approximately vertical but 
extremely irregular bodies extending down into the mass of the limestone. Other important mines of this type are 
(4) the Florence group, on Printer Boy hill, north of Iowa gulch; (5) the Long & Derry group, on the opposite 
side of the gulch, and on Breece hill (G) the Highland Chief group, overlooking Evans gulch. On Yankee hill are 
the Andy Johnson, Chieftain, Scooper, and others. While in Stray Horse gulch the Double Decker and adjoining- 
mines have gold ore in the lower quartzite, the Adelaide and Argentine find carbonates of lead at the contact of 
the White porphyry and the upper portion of the Silurian formation. 

Minerals. —The most common minerals are cerussite, anglesite, pyromorphite, and galena; chloride, chloro- 
bromide and rarely iodide of silver; iron, generally as hydrated sesquioxide, but in the Breece iron mine as red 
hematite and magnetite, also in the deeper workings in the form of pyrite; manganese generally as a sort of 
wad, and frequently also as pyrolusite; zinc as calamine or silicate, and in depth as zincblende; bismuth as 
sulphide and as sulpho-carbonate in the Florence mine; vanadium as dechenite, or vanadate of lead and zinc, in 
the Morning Star and Evening Star mines. More rarely, native sulphur is found as a decomposition product of 
galena; also native gold and silver in the limestone deposits. Arsenic and antimony show themselves in the 
products of the smelters, the former very persistently, but are seldom found as definite minerals in the ores. 

Outside the California district, the principal mine is the Homestake, on Homestake peak, in the northwestern 
corner of the county, which was developed before the discovery of the silver ores of Leadville. It is a rich body 
of argentiferous galeBa in Archaean gneiss, and is said to have produced at one time a considerable quantity of 
nickel ore in the form of an arsenical nickel mineral supposed to be gersdorffite. A number of less important mines 
have been developed along the western slopes of the Sawatch range in the Archaean which have produced small 
quantities of pyritiferous ores carrying galena. Their main value lies in the silver which they contain, which is also 
accompanied by a ceitain amouutof gold. They are mostlyreduced in the amalgamating mills which have been erected 
at Leadville for treating the few siliceous ores of the district which are free from lead. The comparative poverty 
of the mineral deposits of this district in gold is remarkable when one considers the exceptional richness of 
many of its placers. In the normal silver deposits of Leadville gold is present, if at all, in very minute quantities; 
so that it is not detected by the assayer, but is only found concentrated in the bullion. That it exists, however, is 
proved by its having been found occasionally in the state of native gold in the limestone deposits; for instance, in 
those of the Florence mine. 

GUNNISON COUNTY. 

Gunnison county lies to the west of Lake and Chaffee counties, its eastern boundary being formed by the crest 
of the Sawatch range. It originally included only the mountainous country connected with this range and the 
group of the Elk mountains which branch off from it in a northwesterly direction. Since the recent cession of the 
lands of the Ute Indian reservation it also includes a large portion of this reservation in the Colorado plateau 
region, extending to the boundary of Utah. Its present area of 11,338 square miles is greater than that of any 
county in the state. 

The plateau region, as yet comparatively unexplored, is mainly occupied by nearly horizontal beds of Cretaceous 
and Tertiary age. Except, therefore, where the underlying Archaean rocks have been exposed by deep erosion, or 
the later formations have been traversed by masses of eruptive rock, this region affords little promise of return 
to the prospector in his search after deposits of the precious metals. In the eastern mountainous region, on the 
other hand, the geological conditions are such as to lead one to expect widespread and important deposits of 
metallic minerals. Owing to its isolated condition, being separated from the rest of Colorado by high mountain 
ranges whose lowest passes are over 10,000 feet high, and having been but recently reached by lines of railroad, but 


78 


PRECIOUS METALS. 


few actually producing mines have yet been developed within its limits. In spite of the fact that it is penetrated by 
two lines of railroad, the Denver and Rio Grande and the Denver and South Park, its conditions would be unfavorable 
for the treatment of low-grade ores—the true source of wealth of a mining region—on account of the high grades which 
have to be overcome by these roads in reaching it, and which, therefore, enhance the cost not only of supplies, but of 
the movement of ore and fuel, were it not for the fact that it contains within itself the means for treating its own 
ores at low cost in its coal beds, which are not only exceptionally well situated for mining, but are of a quality 
probably superior to any on the eastern slope of the mountains. On the completion of the extension ot the former 
road to Utah it will have an additional outlet in that direction, free from the drawback of exceptionally heavy 


grades. 

The geology of the western slope of the Rocky mountains presents certain contrasts to that of the eastern. In 
the latter region, although along certain shore-lines, by unequal erosion, beds of different horizons are found abutting 
against the underlying Archman, in general the lowest Cambrian beds are those which rest directly upon it. In 
the western region, on the other hand, erosion discloses crystalline gneisses and granites, presumably belonging 
to the Archman, in direct contact with horizons as high as the Cretaceous, and at points far removed from any 
well-defined shore-line. The sedimentary beds also differ somewhat in lithological constitution, and are, as a rule, 
considerably thicker than corresponding beds on the eastern slope. Again, the coal-forming period, which on the 
eastern slope was at the very close of the Cretaceous (or, as some have maintained, at the commencement of the 
Tertiary), in the western region, to judge from the testimony of the thickness of beds overlying it, occurred 
considerably before the close of this epoch. The ore deposits also, which there are found mainly in the Archmau or 
Palaeozoic formations, in the Gunnison region are found to occur also in the Mesozoic formations even as late as the 
uppermost portion of the Cretaceous. The bituminous coals of the Cretaceous formation, which are generally called 
lignites , but not it seems with absolute propriety, are here locally transformed into semi bituminous and even into 
anthracite coals of excellent quality. 

The geological structure of the Elk Mountain region is one of such extreme complexity that only the barest 
and most general outlines can be presented in the limited space here allotted. According to Mr. W. H. Holmes, its 
structure is that of a great fault-fold, i. e., an anticlinal fold, running generally with the axes of the range and 
broken along its crest by a fault, the eastern slope of the anticlinal being relatively gentle, but the western so 
steep that in one portion the beds are actually inverted. Of the sedimentary beds involved in this fold only the 
Carboniferous, Trias, and Jura have escaped erosion in the higher portion of the mountains, while the Cretaceous 
beds are left along its Hanks. In the center of this fold Mr. Holmes places a mass of eruptive granite. The writer 
has had no opportunity of verifying Mr. Holmes’ observations in the center of the range, but is quite ready to accept 
his solution of the structural problems involved, while making a mental reservation as to the existence of eruptive 
granite at this point. From observations made during a hasty visit to the southern slopes of the range along Slate 
creek and the heads of Ohio and Anthracite creeks he is inclined to think that this eruptive body may belong, as 
do the eruptive masses there, to the porphyries of Mesozoic age and of the Mount Lincoln type, already described 
in the section on Park county. These rocks here break through the Cretaceous strata, not only in narrow and 
well-defined dikes, but in immense masses, forming entire mountains of most picturesque outline, of which Crested 
butte and Gothic peak form the simplest type, relics of nearly horizontal Cretaceous strata extending up their 
sides for several hundred feet above the bottoms of the present valleys. These porphyries in the region visited 
are indicated on the Hayden map either as eruptive granites or as Tertiary volcanic rocks. Since they break through 
the Cretaceous beds, they must have been erupted in post-Cretaceous times, but probably before the deposition of 
any distinctly Tertiary beds, and their mode of occurrence and lithological characteristics are quite different from 
those of Tertiary volcanic rocks. The intrusion of such enormous masses of molten material has produced an 
extensive and widespread metamorphism of the sedimentary beds, and may probably account for the change of the 
bituminous coals to anthracite. 

The Elk mountains are evidently of later age than the Sawatch, and, very possibly, even later than the Mosquito 
or Park range. The ore deposits of the Ruby district must be of post-Cretaceous age, since they traverse Cretaceous 
rocks; but as to the age of deposits occurring in the older rocks no data are yet at hand. Ore has been found 
in almost every portion of the Elk mountains and on the flanks of the Sawatch. The principal mining centers are 
Aspen, on the northeast slope of the Elk mountains, and Independence, on the west slope of the Sawatch, in the 
drainage of Roaring Fork; Ruby, Gothic, and a number of small towns on the southwest slope of the Elk mountains ; 
and Pitkin and Tin Cup, on the southwest slope of the Sawatch. At Independence sulpliuret ores carrying silver are 
found in the Archman. The Gold Cup mine, near Alpine pass, in the Tin Cup district, occurs in a black, fine-grained 
limestone, not unlike the Carboniferous limestones of the Mosquito range. Its ore is a silver-bearing eerussite, 
associated with some oxide of copper in a ferruginous and siliceous gangue. Of the ore deposits occurring in the 
Cretaceous rocks in Ruby district the Forest Queen mine may be taken as a type. The vein material seems to be 
a decomposed porphyry; probably a narrow dike traversing the Cretaceous sandstones, and standing in an 
approximately vertical condition. The ore is largely ruby silver and arseuical pyrite, occurring in small crevices and 
fissures in the decomposed porphyry. The gangue material is sometimes simply an indistinctly banded quartz. 


GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


79 


CHAFFEE COUNTY. 

Chaffee county occupies the valley of the Arkansas river between the crests of its bounding ranges from the 
southern boundary of Lake county down to Fremont and Saguache counties, a little below the mouth of the South 
Arkansas. Its mountain slopes are composed of Archaean rocks, mainly granite, traversed by porphyry dikes, 
with occasional remnants of Palaeozoic formations in the southern parts which have escaped erosion resting 
on their crests. The valley bottom, as in Lake county, contains stratified beds of gravelly formation and of recent 
date; but whether they are of the same age as the Lake beds of Lake county, or have been formed in the Tertiary 
period, is not yet definitely known. The more recent gravel deposits at the mouth of the larger canons, as well 
as those along the bed of the Arkansas river, yield gold. The richest are those at Cash creek, which have been 
worked since the earliest discovery of minerals in this portion of the country. 

Its mining districts have but few developed mines, hence data with regard to them are extremely meager. 
In the neighborhood of the town of Granite gold-bearing veins have been worked on the east side of the valley in 
former years. Near Buena Vista, also on the east side, is the Free Gold district, so called from the Free Gold mine, 
which is an auriferous quartz vein in a syenite containing abundant titanite. The foot-wall specimen differs from 
that of the hanging wall, which suggests the possibility that the vein may be on a fault-plane. 

The Chalk Creek district toward Alpine pass, on the opposite side of the valley, shows also syenitic country 
rock which contains a little quartz. The mines from which specimens were obtained are the Black Hawk, Mary 
Murphy, and Hortense. The vein material of the two former is a felsitic mass which may be a decomposed porphyry. 
In the ore specimen the only recognized minerals are pyrite and a black mineral which seems to contain manganese. 
The ore of the Hortense is a decomposed quartz-porphyrv, from which some metallic mineral has been removed by 
solution. 

The Monarch district is near the head of one of the branches of the South Arkansas river. The Monarch mine, 
from which its name is derived, is a limestone deposit, occurring between a dark-gray limestone above and a fine¬ 
grained white limestone below. The horizon of these limestones is not known, but it is very possible that they 
correspond to the Blue and White limestones of Leadville. The ore, like that of Leadville, is mainly cerussite or 
carbonate of lead. The Columbus mine, in the same district, occurs in granite, its ore consisting of fragments and 
crystals of quartz, cemented together by some metallic mineral colored red or yellow by oxide of iron. 

DOUGLAS COUNTY. 

Douglas county lies south of Arapahoe county, and extends as far as the divide between the Platte and Arkansas 
rivers and east of Jefferson county, including a portion of the Colorado range lying east of the Platte canon. As 
is the case further north, this portion of the range is not yet found to contaiu valuable metallic minerals. The 
coal rocks, however, underlie the plain country east of the foot-hills, though as one approaches the divide they are 
more and more deeply buried beneath the Tertiary deposits of which this mesa-like ridge is formed. Their outcrops 
can be traced from the Platte canon to the southern borders of the county, approaching nearer and nearer to the 
foot-hills as one proceeds southward. 

In the neighborhood of Castle Rock are mesa-like ridges, which extend almost continuously to the eastward; 
but west of the railroad, and between it and the foot-hills, these ridges are broken by erosion into a series of isolated 
buttes, and are made up of gravel and coarse conglomerate derived from the Arclnean formation, belonging to the 
Monument Creek Tertiary of the Hayden survey, whose age has not yet been determined. In the neighborhood of 
Castle Rock, and for some six or eight miles to the southward, the surfaces of these mesas are covered by a light 
pinkish-colored rhyolitic tufa, which forms an admirable building-stone, and has been very extensively used for 
this purpose in Denver. The outlines of this volcanic flow have not yet been accurately determined; it extends 
but a short distance east and west, and has an average thickness of about 20 feet. 

EL PASO COUNTY. 

More than half of the area of El Paso county, which lies to the south of Douglas, is plain country. Its western 
mountainous area includes the partially isolated mass of Pike’s peak, separated from the main Front range by Dte 
pass and Manitou park, which once constituted a bay or arm of the Palaeozoic sea. 

The only mineral of industrial importance thus far developed is coal, of which working mines exist to the east 
of Colorado Springs. Prospectors after the precious metals on Pike’s peak have, however, developed an extremely 
interesting series of minerals, of which those ot the cryolite group may possibly prove of economic importance. 
The following are the species previously recognized: 

Microcline, as green amazon stone and other colors; albite; biotite, var. siderophyllite; quartz, clear and 
smoky; fluorite; columbite; gothite; hematite and limonite as pseudomorphs after siderite; arfvedsonite; 
astrophyllite; zircon. 

In addition to the above the following have recently been determined by the members of the Rocky Mountain 
division of the United States geological survey: 

Topaz, plienacite, kaolinite, a peculiar green muscovite, cryolite, thomsenolite, gearksutite, and other fluorides 
not yet definitely determined. 


80 


PRECIOUS METALS. 


FREMONT COUNTY. 

Fremont county, which lies to the east of Chaffee aud Saguache counties, includes the canon valleys ot the 
Arkansas after it bends to the eastward and a portion of the plain country beyond Canon City. Its mountains 
have a base of Archaean, which in the western portion of the county is covered by Palaeozoic formations, and on the 
north, toward the South park, by Tertiary eruptive rocks, with probably some older porphyries. Along the toot-hills 
at Canon City occur the upturned Triassic and Cretaceous rocks, which furnish valuable building-stones. A 
limestone of the Colorado Cretaceous, which is remarkably pure, is used in making lime and as a flux for smelting 
works. From less pure limestone above the Triassic hydraulic cement is made. From Jurassic aud Lower 
Cretaceous beds in the plains, as well as in the valley of Oil creek, petroleum has been obtained, and several wells, 
some over 1,000 feet in depth, have been sunk. As yet no considerable concentrations of oil have been developed. 
South of Canon City is a syncliual basin in which the Laramie beds have escaped erosion, and where valuable coal 
mines have been opened by the railroad companies. 

CUSTER COUNTY. 

Custer county lies to the south of Fremont, and comprises the Wet Mountain valley, lying between the Wet 
mountains or Greenhorn range on the east and the north end of the Sangre de Cristo range on the west. The 
former mountains are a southern continuation en echelon of the Front or Colorado range, and consist of Archsean 
rocks, mainly granite, with Mesozoic formations resting against its eastern base. This range is relatively low, and 
its slopes gentle, except where cut through by deep canons. The Sangre de Cristo range, on the other hand, which 
is a southern continuation, also en echelon , of the Mosquito or Park range, is a lofty imposing chain, whose rugged 
outlines suggest a very different composition. It has not been examined by the writer, but presumably consists of 
the same Palaeozoic rocks that are found in the Mosquito range, resting on an Archaean base and traversed by 
Secondary eruptive rocks, of which the so-called Sangre de Cristo granite, outlined on the Hayden map, is very 
possibly a variety. The Wet Mountain valley at its widest point comprises a distance of over 20 miles from east to 
west between the crests of these bounding ridges. The valley bottom lies near the west side of this depression, its 
Quaternary covering resting either on the Archaean, or on the eruptive rocks which have broken through it. 

The principal mines have been developed in the neighborhood of the towns of Silver Cliff and Eosita, and an 
area of 10 miles east aud west and G miles north and south includes the greater portion of these. In this area the 
underlying Archaean is broken through and covered by Secondary eruptive rocks, among which diabase is the only 
type which has as yet been definitely determined. To these eruptions have succeeded flows of andesite and 
rhyolite, which outcrop at Eosita and Silver Cliff. 

The town of Eosita is situated near the eastern end of the district, in the midst of a group of steep hills with 
smooth rounded slopes, which project out into the valley from the Wet Mountain range. The town of Silver Clift’, 
about six miles west of Eosita, is situated on the open plain near a mesa-like iklge, on whose cliff face, from 
which the town derives its name, are found the silver deposits of the Eacine Boy mine. The rock of which this 
cliff is formed is a light pinkish-colored rhyolite, showing the characteristic finely laminated or fluidal structure. 
In the town itself, and along the eastern edge of the cliff, are outcrops of a dark pitchstone, probably a hyaline 
variety of the rhyolite. Outcrops of granite are found on the plains between Silver Clift' and in the hills around 
Eosita, rendering it probable that the rhyolite rests directly on the underlying Archman. A number of isolated 
hills rise out of these plains, the most prominent of which is Eound mountain, on which is situated the Plata 
Verde mine, and about two miles to the northward are the Blue mountains, in which is situated the Bull-Domingo 
mine. The bottom of the valley, through which runs Grape creek, lies still to the west of Silver Cliff, and has a 
considerable extent of arable land. 

Ore deposits. —The ore deposits of this region are in many cases rather exceptional in character, and have 
given rise to considerable speculation as to their origin. As yet, however, no systematic or exhaustive study has 
been made of them on which to found a definite and satisfactory classification. Most prominent and remarkable are 
the Bassick and the Bull-Domingo, each situated near the northern limits of the eruptive rocks, the former a short 
distance north of Eosita, the latter 7 miles westward, correspondingly situated with regard to Silver Clift’. The 
characteristic feature common to these two mines is that the ore is found in large bodies without any definite 
boundary, forming a coating on irregularly-rounded fragments of the country rock. A favorite method of accounting 
for this mode of occurrence has been that the ore cavities are old craters or solfataric openings, in which the 
fragments of country rock have been tossed about and rounded by attrition and coated by a deposition from metallic 
vapors and solutions. While the known facts with regard to these deposits are insufficient to afford a positive 
theory with regard to their origin, the evidence is decidedly against this somewhat startling hypothesis. The 
country rock of the Bull-Domingo mine is a hornblendic gneiss, and therefore probably belongs to the 
Archaean. The ore, which is mainly an argentiferous galena, forms a regular semi-crystalline coating from one- 
eighth to one-quarter of an inch in thickness around the bowlders and pebbles of country rock, and fills the irregular 
interstices between them. These pebbles are not in direct contact one with the other, but are separated by the 
metallic coating belonging to each individual pebble. The galena is frequently covered by a second botryoidal 


GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


81 


coating, probably of a siliceous nature. The deposit is from 40 to GO feet wide, and strikes in a northwesterly 
direction. No fresh specimens of the country rock of the Bassick mine were obtained, and its exact nature is not 
therefore known. It is said to be the same on both sides of the deposit, and to be an eruptive rock. In this case it 
is probable that it is a breccia, and the ore is a replacement of the matrix. According to Mr. L. It. Grabill, (a) the 
deposit is an irregular opening, nearly elliptical, in horizontal sections from 20 to 100 feet in width, and standing 
generally vertical to the depth of present developments, i. e ., about 800 feet. The fragments of country rock 
which till this opening vary in size from one and a half feet in diameter to the.smallest dimensions. They are rarely, 
if ever, in actual contact with each other, while the metallic shells which surround them are tangent. The size of 
the fragments, as well as the quantity of ore or metallic mineral present, decreases from the center outward, without 
any defiuite limit having yet been determined. In the shell or metallic coating which surrounds these fragments 
Mr. Grabill distinguishes a series of concentric layers, the innermost and thinnest consisting of a mixture of sulphides 
of lead, antimony, and zinc, carrying about GO ounces of silver and from 1 ounce to 3 ounces of gold to the ton. 
This layer is always present. A second coating, not always found, is lighter in color, and contains more lead, silver, 
and gold. The third shell is mainly sphalerite or zincblende, reaching a maximum thickness of 5 centimeters, 
which carries from GO to 100 ounces of silver, and from 15 to 50 ounces of gold to the ton, with considerable iron, and 
some copper. This constitutes the principal pay-ore of the mine. The fourth coating, when present, is formed 
of chalcopyrite, but is much more irregular than the previous ones, and carries as high as from 50 to 100 ounces 
of gold and silver. Outside of these a fifth thin coating of pyrite crystals is occasionally found. All the layers 
have a more or less crystalline structure. The remaining interstices between the pebbles are filled with kaolin. 
Another singular fact connected with the deposit is the occurrence of small fragments of charcoal in cavities between 
the bowlders toward the outer edges of the ore body, and most commonly near the water-level. These are sometimes 
partially mineralized, and at others are perfectly unaltered and retain the woody structure. The greatest depth at 
which they have been found is 765 feet from the surface. The other minerals found in^the mine are calamine, 
smithsonite, jamesonite, tetrahedrite,, free gold, and tellurides of silver and gold in minute quantities. 

Another type of deposit iu the region fills more or less vertical fissures traversing the eruptive rocks which form 
the hill country around Rosita. The principal of these is the Humboldt-Pocahontas vein, running northwest and 
southeast, a short distance north of the town. The exact character of the country rock is not definitely known. 
This ore carries chalcopyrite and fahlerz, with a little siderite, iu a gangue of barite. 

The Racine Boy mine, near Silver Cliff, forms a third distinctive type, and seems to be an irregular impregnation 
of the country rock, the ore in general showing a little black staining of some manganese mineral as its only visible 
metallic constituent. Thin films of chloride of silver are sometimes distinguishable. This is a free-milling ore of 
comparatively low grade, but valuable on account of its great mass. Plata Verde mine has not been worked since 
its mill was finished, aud no data are available in regard to the character of its deposit, which is, however, in rhyolitic 
rock. The ore is chloride of silver, with some sulphurets, impregnating the country rock. The Terrible mine, in the 
Archajan, is about 12 miles northeast of Silver Cliff, and has a foot wall of fiue-graiued iron-stained gneiss. The 
vein strikes N. 20° W., and dips 78° NE* Its ore consists of a massive cerussite, sometimes cementing fragments 
of wall rock, the gangue material being decomposed country rock. The Gem, a newly-opened mine some 12 miles 
north of this district, is interesting as having afforded specimens of a rich nickel ore. On Grape creek, in the 
northern portion of the county, a considerable body of titaniferous magnetite has also been discovered. Both these 
last-named deposits are probably in the Arclnean. 

Ore deposits have also been developed on the east slope of the Sangre de Cristo range about 7 miles west of 
Silver Cliff. The Verde mine has a vein striking N. 50° W., and dipping G0° SW., said to be in granite. Its ore is 
a mixture of pyrite and chalcopyrite, with fahlerz. 

HUERFANO COUNTY. 

Huerfano county, lying south of Custer and Pueblo, is largely a plain country, and only its eastern end, which 
includes Huerfano park, a southern continuation of the Wet Mountain valley, extends into the mountain region. 
The surface of the plain country, as well as the bottom lands of Huerfano park, which was a bay in the original 
Archman shore line, is covered by Cretaceous deposits; and it is only along the crests of the bounding ridges, the 
Wet mountain and the Sangre de Cristo, and near the eruptive mass of the Spanish peaks, that the rocks liable to 
carry metallic minerals are exposed. 

The schedule reports furnish data from only a single mine, the Mountain Monarch, in the Third Judicial 
district. This mine is situated on the north slope of the West Spanish peaks, about 10 miles south of La Veta. Its 
deposit is said to be a fissure vein running east and west, with a shallow dip south, and is from 3 to G feet wide. 
The ore is a banded vein material, consisting of galena, pyrite, chalcopyrite, and fahlerz. The country rock is said 
to be granite, and the gangue material porphyry. No specimens of either were sent in, but it seems probable to the 
writer that both belong to the crystalline quartz-porphyries, whose mode of occurrence has been already described, 
and which correspond with what is known of the eruptive mass of the Spanish peaks. 

■ a Trans. A. I. M. E., August, 1882. 

VOL 13-6 








82 


PRECIOUS METALS. 


THE SAX JUAN KEGION. 

Geology.— The San Juan mining region, which embraces San Jnan county, with the adjoining counties ot 
Hinsdale, Ouray, La Plata, and portions of Bio Grande and Conejos counties, takes its name from the San Juan 
mountains, a lofty and irregular mass, which, like the Elk mountains, have a general northwest trend, but are of 
still more irregular structure, and have an even greater predominance of eruptive rocks. Owing to the prevalence 
of the latter, which constitute the mass of a great portion of the mountain region, the structure of the sedimentary 
beds is necessarily very indistinct, and the geological data which are obtainable are of the most unsatisfactory 
nature. The eruptive rocks occur in great masses, sections 2,000 and 3,000 feet thick being shown in the different 
canons, their most characteristic and striking feature being the occurrence of immense breccia beds over wide 
areas throughout the region. The entire mass of these rocks lias been classed by the members of the Hayden 
survey among the Tertiary eruptives, and they have been colored on the map as either trachytes or basalts. 
While basalts undoubtedly do occur, and trachytes may be found, these or later flows cover bodies of earlier 
eruptive rocks, and it seems probable to the writer that hiie deposits in the region will be found to occur mainly 
in the latter. This idea is supported by the examination of the specimens of the country rock brought in by census 
experts. Although these specimens were mainly in a condition of alteration so far advanced—as is common among 
eruptive rocks in the neighborhood of mines—that their original condition could rarely be definitely determined, 
some undoubted porphyries, diorites, and diabases occur among them, and the others can be referred, with more 
or less probability, to varieties of one of these types, while among the eighteen specimens which were examined 
microscopically only a single undoubted Tertiary rock (basalt) was found. This occurs as the foot wall of the Ohio 
Consolidated mine, in Hinsdale county. In some of the valleys erosion has exposed granite and gneiss, presumably of 
Archman age, underlying these eruptives. At the head of the Uncompahgre river, near Ouray, beds of Palaeozoic and 
Lower Mesozoic age are found resting on the granite and sinking to the northwest under the Cretaceous formations. 
The latter cover the western portions of the counties of Ouray and La Plata, which, like those of Gunnison and 
Grand counties, belong to the Colorado plateau region. On the southern slopes of the San Juan mountains, in San 
Juan county and the northeastern corner of La Plata county, there is exposed a considerable area of Palmozoie rocks, 
which to the southward pass under the Cretaceous formations of the valley of the San Juan. A large portion of 
these are of undoubted Carboniferous age, but adjoining the valley of the Animas, on the east, is a mountainous 
region called the Quartzite peaks, composed of rocks whose age is a matter of considerable uncertainty. The 
limestones which adjoin the quartzite have been considered by Dr. Eudlich as Devonian mainly on tlie evidence of a 
siugle well-defined fossil. This fossil is, however, pronounced by Professor I\. P. Whitfield to be a Carboniferous and not 
a Devonian type. The quartzite formations, which are supposed to underlie these, are called on the map Metamorphie- 
Palceozoic, the rubric of this formation, however, being included in the Archaean; a seeming contradiction of terms 
of which the writer has found no explanation. It is probable that the Palaeozoic formations thicken to the southward, 
as they are known to do to the westward; and since the Devonian is well developed in Utah and Nevada, and fossils 
of the Waverly type have recently been found in Lake valley, New Mexico, it is very possible that this formation 
may be represented in the region, but its existence cannot yet be considered as determined. 

Gee deposits. —The most striking feature in the mineral development of the San Juan region is the immense 
quartz veins traversing the eruptive rocks, which stand nearly vertical, their outcrops projecting like walls from the 
surface, and often traceable to a depth of several thousand feet along the sides of the deep valleys and canons. 
According to Mr. B. C. Hills, these veins cross both the older eruptive rocks and what he considers as the overlying 
Tertiary eruptives; but it is only in rare instances that the latter have been shown to inclose valuable ore bodies, 
these being found generally in the older massive or brecciated rocks, whose prevailing color is some shade of green. 
Veins are also found in the underlying gneiss and granite; and in the western portion, especially in the neighborhood 
of Eico, are deposits in limestones of Carboniferous age, frequently along bedding-planes and at the contact with 
sheets of intrusive igneous rocks. 

The deposits of the region are mainly argentiferous. In some, however, gold is the chief pay mineral; in 
others both gold and silver occur. Free milling gold ores are, as a rule, comparatively rare, the majority of the 
ores containing a large admixture of base metals, so that they require smelting. The prevailing minerals are 
argentiferous galena, gray copper, generally argentiferous or freibergite, and, in the upper part of the deposits, 
native silver and pyrargyrite or ruby silver. Bismuth-silver minerals are found in several mines in considerable 
quantities. Gold is apparently derived in most part from pyrite. Barite is not uncommon as a gangue material, 
and fluorite also occurs, although more rarely. Compounds of antimony and tellurium are said to occur, and rarely 
molybdeuite and some nickel minerals. The veins are said to have a banded structure, and the quartz is said to 
be crystalline. It must be noted, however, at the same time, that in many cases one or both walls are not well 
defined, and a portion at least of the vein material is quite frequently decomposed country rock. Of the age of 
these deposits, in the uncertainty which exists as regards the true character of the various country rocks, but little 
can be definitely said. Mr. Hills, who has devoted considerable study to ore deposits, especially those of Ouray 
county, divides the veins into three systems, which he regards as distinct and probably of different age: First, 
silver-bearing veins, standing at high angles (80° to 90°) and thin (6 inches to 3 feet wide), with no gouge or 


GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


83 


selvage, carrying essentially base-iyetal ores. Second, gold-bearing veins, large and strong, dip about 00°, gouge 
or selvage on one or both walls, intersecting the former, and therefore of later age. His third class differs from the 
first only in being wider and stronger and in carrying their ore in persistent bands or streaks. Like them, they 
stand at a high angle, and sometimes carry bismuth and antimony minerals. These veins are essentially gold-bearing, 
as even when carrying base-metal ores they contain little or no silver. According to Mr. T. B. Comstock, in an article 
on the geology of San Juan county, (a) the age of the veins of the district is probably post-Tertiary, and in their 
gradually varying strikes, in which there is little evidence of any systematic parallelism, he finds a tendency to 
radiate out from certain points which he considers centers of tmchytic eruption. As, however, in the nomenclature 
and classification of eruptive rocks, he follows a system adopted by Dr. Endlich, and which is peculiar to that 
gentleman, the writer is at a loss to know wliat value to place on his evidence. He recognizes a primary and 
secondary system of veins, the latter of which cross the former, and makes the following provisory classification: 
First, those having a northwest trend, which are pre-eminently gray copper (freibergite) lodes ; second, those with 
an east and west trend, the bismuth series of lodes, carrying occasionally nickel and molybdenum minerals; third, 
those with a northeast trend, the telluride series, with antimony and sulphides of the precious metals. From the 
data gathered by census experts, which are necessarily very incomplete, it appears that in San Juan county the 
northwest trend predominates; in the Uncompahgre district, comprising the northern portion of San Juan and the 
adjoining portion of Ouray county, the northeast trend predominates; while in Ouray county these two directions 
are about equally distributed, the east-and-west trend being in either case of subordinate importance. 

SAN JUAN COUNTY. 

San Juan county has ail area of only 5G0 square miles, and includes the drainage area of the head of the Animas 
river. Its mines are principally found in the lofty peaks which surround the picturesque and elevated basin of 
Baker’s park and its tributary valleys. They occur mainly in the older eruptive rocks, which here apparently rest 
directly on a base of gneiss and crystalline schists, presumably of Archaean age. 

From Baker’s park southward the Animas flows in deep canons cut through later sedimentary rocks, which 
on the east consist mainly of the questionable series classed as Mctamorphic-Palaeozoic, and on the west of limestones 
of Carboniferous age. Of the later eruptive rocks which cover those of Secondary age it can only be said that, in 
view of the facts developed by recent more exact lithological studies, it is unfortunate that the term u trachyte’ 7 
should have been so universally applied, inasmuch as late investigations of other districts where this rock was 
supposed to exist in large masses prove the normal type to be of extremely rare occurrence. 

The mines reported by census experts belong to three principal districts: the Animas district, about Baker’s 
park and Silverton; Eureka district, in the northeast portion of the county; and the Uncompahgre district, on the 
mountains between the Uncompahgre ana Animas rivers, which apparently takes in also a portion of Ouray county. 
The region is undoubtedly one of exceptional richness in mineral developments, so that Mr. Comstock’s statement 
that one-sixth of the area of the county is taken up by lode claims seems scarcely an exaggeration. The subjoined 
table gives a brief summary of the data obtained from producing mines by census experts: 


Mine. 

AX1MA8 DISTRICT. 

Aspen Group. 

Bowery. 

Cleveland Consolidated. 

Diamond (Emblem lode) 

Empire. 

Hercules. 


Country rock and vein. 


Greenish, indistinct porphyritic rock. Undetoiiuinabie. Vein : 
strike, NW.; dip, 80° SW.; width, 4 feet. 

Altered felsite-porphyry. Vein: strike, N. 80° E.; dip, 80° S.; 
width, 10 feet. 

Diorite (diabase ?). Contains fibrous uralitic hornblende, which 
may have come from augite: chlorite, epidote, and calcite as de¬ 
composition products. Vein: strike, N. 27° W.; dip, 75° W.; 
width, 4 feet. • 

Dioritic (?) rock with quartz in small grains. Vein vertical; 
strike, NW.; width, 4 feet. 

Quartz-bearing hornblende-diorite. Vein: strike, N. 45° W.; 
dip, 86° SW.; -width, 7 feet. 

Diorite? (called syenite). Vein: strike, NW.; dip, 82° SW.; 
width, 10 feet. 


Highland Mary. Biotite-gneiss. A dike of quartz-porphyry cuts the vein at, right 

angles. Vein vertical; strike, N.62° W.; average width, 10 I 
feet. 


Jennie Parker. 

Molas. 

North Star (Sultan mountain).. 

North Star (Sing Solomon 
mountain). 


Diorite? (called syenite). Vein: strike; NW.; dip, 80° SW.; 
width, 5 feet. 

Hanging wall white indistinctly stratified rock, consisting of j 
quartz and feldspar—between a quartzite and a gneiss; foot j 
wall decomposed porphyry. Vein vertical; strike, NE.; 
width, 6 feet. 

Very much decomposed porphyry. Vein: strike, N. 36° W.; J 
dip, 65° SW. 

Greenish felsitic rock (diorite?). Vein: strike, N. 47° E.; dip, j 
74° NE.; width, 40 feet. 


Ore and gangue. 


Galena and cerussite, with gray copper, rich in silver (frei¬ 
bergite). 

“ Carbonate ” ore in quartz, with incrustations of ocher, azu- 
rite, and malachite. Gangue: altered country. 

Massive freibergite in gangue of calcite and dolomite, with a 
little galena. 


Mixture of galena, freibergite, and chalcopyrite, with barite 
between quartz layers, forming banded veiu material. 

Freibergite, galena, pyrite, and chalcopyrite in quartz. 


Freibergite, pyrite, and some galena carrying silver. 


Galena, freibergite, and chalcopyrite carrying silver, with trace 
of gold. 

Argentiferous galena, freibergite, and chalcopyrite. Quartz, 
gangue. 

Galena and barite, with stains of copper minerals. 


Massive argentiferous galena, freibergite, and zincbfentfe, with a 
little pyrite. 

Argentiferous galena and cerussite, with freibergite. 


a Trans. A. I. M. E., August, 1882. 









































84 


PRECIOUS METALS. 


Mine. 

Country rock and vein. 

- r 

Ore and gangue. 

LAS ANIMAS DISTRICT—COnt'd. 



Philadelphia. 

No specimen. Called “ trachyte”. Vein: strike, NW.; dip, 71° 
SW.; 2J feet wide. 

Freibergite; a little galena, with silver and some gold, in quartz 
gangue. 

Pride of the West. 

Dark green compact decomposed rock, in part breccia. Undeter¬ 
minable. Vein: strike, NW.: width, 28 feet. 

Massive argentiferous galena, with chalcopyrite and freibergite. 

EUREKA DISTRICT. 



Adelphi. 

Quartz-free plagioclase- rock, with crystalline groundmass, 
probably diorite. Basic silicate changed to chlorite and calcite. 
Vein : strike, NE.; dip, 78° SE.; width, 3 feet. 

Massive freibergite, with barite and some chalcopyrite. 

Big Giant . 

White quartz-porphyry. Vein: strike, N. 50° E.; dip, 45° SE.; 
width. 23 feet. 

Freibergite, argentiferous galena and pyrite, with quartz. 

Bonanza tunnel. 

Porphyrite, with biotite, aud probably hornblende, and a little 
quartz. Much calcite in tilins. 

Occurs in two parallel veius, one carrying galena, the other frei¬ 
bergite and barite. 


Diorite? Vein: strike, !NE.: dip, 86° SE. 

Freibergite, with some galena and pyrite. 

Massive argentiferous galena, with layers of quartz parallel to 
the cube faces; zincblende, pyrite, and chalcopyrite also occur. 

Mastodon. 

Decomposed greenish rock (diorite?). Vein: strike, N. 40° E.; 
dip, 70° SE.; width, 200 feet. 

Sioux City...... 

Greenish decomposed rock (diorite?). Vein: strike, N.; dip, 78° 
E.; width, 4 feet. 

Mainly galena ; some gray copper. 

Tom ilooro. 

Greenish decomposed rock (diorite). Vein nearly vertical; 
strike, NE. : width, 60 feet; pay streaks, 9 inches to 5 feet. 

Argentiferous galena and zincblende; massive. 

UN^OMPAHGRE DISTRICT. 


Alabama. 

Greenish eruptive rock, with porphyritic crystals and included 
fragments of red quartzite. Vein: strike, NE.; dip, 70° E.; 
width, 25 feet. 

Argentiferous galena and freibergite, with some pyrite and 
chalcopyrite. Gangue: quartz and feldspar. 

Alaska. 

Diorite or iliabase microscopically similar to that of the Adelphi. 

Chiedv freibergite, with some galeua, aud containing bismuth-sil- 


Vein: strike, NE.; dip, 80° SE.; wiilth, 30 inches. 

ver in considerable quantity. 

Annio Wood. 

Hanging wall (?) plagioclase-hornblende rock; diorite (?); foot 
wall (?) much altered porphyritic diabase; groundmass, crys¬ 
talline. Vein: strike, N. 20° to 30° E.; dip, 80° E.; 5feet wide. 

Freibergite, stephanite, ruby silver, sulphide of bismuth with 
chalcopyrite. 

Bonanza. 

Greenish felsite-porphyry much altered. Vein: strike, N. 65° E.; 
dip, 80° SE. 

Freibergite and chalcopyrite with barite. Galena and pyrite also 
found. Quartz gangue. 

Boston. 

Light-colored decomposed porphyry. Vein: strike, N. 20° E. ; 
dip, 70° SE.; width, 4 feet. 

Argentiferous galena with chalcopyrite and zincblende. Gangue: 
quartz and altered country. 

Maid of the Mist. 

Plagioclase rock, with both hornblende and augite. Porphyrite 
or diabase (?). Vein : strike, N.20°E.; dip, 65° E. 

Argentiferous galena, freibergite and zincblende, with chalco¬ 
pyrite and pyrite. Gangue : quartz and altered countiy. 

Mammoth. 

Greenish decomposed porphyry; basic. Vein: strike, N. 10° E.; 
dip, 72° SE.; width on surface, 30 to 60 feet. 

Freibergite, stephanite, ruby silver, native silver, sulphide of bis¬ 
muth, with pyrite iu quartz and altered country. 

Bed Cloud. 

Too much altered for determination. Vein: dip, 75° SE.; width, 

3 feet. 

Argentiferous galeua, freibergite, zincblende, chalcopyrite, and 
pyrite, with some gold in quartz and altered country. 

lied Rogers. 

Greenish country rock; decomposed porphyry. Vein: strike, N. 
50° E.; dip, 80° SE.; width, 4 feet. 

Freibergite, stephanite, ruby silver, with barite and quartz; a 
little galena. 

Saxon . 

Green decomposed porphyry. Vein: strike, NE. ; dip, 85° SE.; 
width, 30 to 40 feet. 

Freibergite, galena, and stephanite (?), with some chalcopyrite. 
Gangue: quartz. 


OURAY COUNTY. 

Ouray county includes the northern and western slopes of the San Juan mountains, with certain outlying 
groups belonging geologically to the same mass, and the plateau country extending westward from thence to the 
Utah line, which is composed mainly of nearly horizontal Mesozoic beds. 

The development of the precious metals has been thus far confined, as might be expected, to the eastern and 
more mountainous portion of the county. In the neighborhood of Ouray, which is near the northwest limit of the 
■eruptive area of the San Juan mountains, erosion has exposed the underlying Palneozoic formations and a small 
area of what is presumably Archaean. The deposits of the northern portion of the TJncompahgre district occur 
mostly in the sedimentary beds, but in general are more or less closely connected with the overlying eruptive rocks. 
The veins belong more generally to the metamorphic type, although there seems to be no marked change in their 
mineral constitution. Mineral Farm seems to be a somewhat exceptionally rich deposit in limestone. In Sneffles 
district to the west of Ouray, in Upper San Miguel district, and in Iron Springs district near Ophir, to the south, the 
veins, like those of San Juan county, are in eruptive rocks, and stand at a high angle, many of them, especially in 
the latter district, carrying considerable gold. In the neighborhood of Rico, still farther south, the ores occur in 
sedimentary rocks, in general parallel with the stratification and with either foot or hanging wall of porphyry. 
They are essentially silver-bearing, aud have a clay gangue material colored by hydrated oxides of iron and 
manganese. 


Mine. 


Country rock and vein. 


Ore and gangue. 


UXCOMPAHGRE DISTRICT. 

Begola.. 

Dexter. 

■Golden Gate. 

Grand View. 


Blue-gray crystalline limestone, witli cliert segregations. Quartz- 
porphyry is said to occur. 

Hanging wall greenish felsite-porphyry, and shale below. Foot 
wall shale, and quartzite below. Vein: strike, N. 20° E.; dip, i 
30° E. with country; width, IS inches. 

White quartzite. Vein: strike N. 20° W.; dip, 80° W.; width, 
4£ feet. 

Sandstone and conglomerate overlaid by eruptive rock, Vein: 
strike, X. 82° W.; dip, 77° S.; 18 inches wide. 


Argentiferous galena, chalcopyrite, and pyrite, with freibcrgite 
and stibnite (?). Gangue: quartz and barite. 

Massive argentiferous galena, native silver, stephanite, zinc- 
blende. Chalcopv rite and pyrite are said to occur. Gangue: 
quartz and altered country. 

Argentiferous galena, freibergite, chalcopyrite, and pyrite in 
quartzite. 

Pyrite and chalcopyrite, carrying gold and silver, impregnating 
country rock. 









































































GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


85 


Mine. 

Conntry roclc and vein. 

Ore and gangue. 

UNCOMPAHGRE DISTRICT—COnt’d 



Riverside. 

Green porphyritic rock called trachyte. Vein: strike, N. 50° 
E.; dip, 78° S.; width, 4 feet. 

Argentiferous galena, with pyrite and a little freibergite. 

Union. 

Gray porphyritic rock called trachyte. Vein : strike, N. 40° W.; 
dip, 80° S.; width, 7 feet. 

Argentiferous galena, clialcopyrite, and pyrite, and some ste- 
phanite. 

SNEFFLES DISTRICT. 


Potosi. 

Greenish felsiticrock, locally called trachyte. Vein : strike, NE.; 
dip, 65° NW. 

Freibergite, stephanite, and argentiferous galena, in white quartz 
and decomposed country. 

Terrible. 

Probably altered diabase. Vein: strike, N. 80° W.; dip, 85° S ... 

Mainly argentiferous galena. Gangue: quartz and altered coun¬ 
try. 

Argentiferous galena, zincblende, and freibergite, with some 
pyrite. 

U. S. Depository. 

Undeterminable brecciated eruptive rock, locally called trachyte 
Vein : strike, N. 37° W.; dip, 75° SW.; width, 5A feet. 

Virginins. 

No specimen; locally called trachyte. Vein: strike, N. 32° W.; 
dip, 80° SW.; width, 4 feet. 

Argentiferous galena and freibergite. Gangue: quartz and al¬ 
tered country rock. 

Wheel of Fortune. 

Porphyritic rock like that, generally called trachyte in the region. 
Vein : strike, N. 5° W.; dip, 05° W.; width, 5 feet. 

Stephanite and freibergite. Gangue: quartz and porphyry. 

Yankee Boy... 

No specimen; locally called trachyte. Vein : strike, Y. 85° W.; 
dip, 85° S. 

Argentiferous galena and zincblende, with barite and chalcopy- 
rite. Gangue: quartz and altered country. 

PIONEER DISTRICT. 



Grand View. 

Hanging wall decomposed porphyry or porphyrite; foot wall blue 
tine grained dolomite. Deposit: dip, 45° to 72° NE., 2 to 14 feet 
thick. 

Oxides of manganese, carrying silver, probably as chloride or 
sulphide. 

Hope.. 

Hanging wall porphyry (?). Foot wall limestone. Vein: dip, 25° 
.NE.; deposit, 1 to 8 feet thick. 

Hydrated iron and manganese oxides, carrying silver. 

Newman. 

Hanging wall dark argillaceous shale. Foot wall porphyry or 
porphyrite. Vein: dip, 8° NW., 6 feet thick. 

Iron-stained clayey mass, carrying silver, carbonate of lead, and 
other minerals. 

UPTER SAN MIGUEL DISTRICT. 



Alta. 

Undeterminable; called trachyte. Dike of altered porphyry(?). 

, Vein : strike, N. 75° W.; dip, 70° N. 

Argentiferous galena and freibergite, with barite' and quartz. 
Several parallel veins. 

Cimmarron. 

Decomposed rock, probably porphyrite or diabase. Vein: 
strike, N. 22° E.; dip, 75° SE.; width, 3 feet. 

Argentiferous galena, freibergite, clialcopyrite and pyrite, with 
some free gold. Gangue: light-colored' felsitic rock, banded 
parallel with walls. 

Gold King. 

Undeterminable. Porphyry (?) Vein: strike, N. 22° E.; dip, 75° 
SE.; width, 3 feet. 

Gold-bearing quartz in altered country rock. 

• 

N.W.H.Jr. 

Greenish brecciated undeterminable eruptive rock called trachyte. 
Vein: strike, N. 1G° W. ; dip, 82° W. ; width, 12 feet. 

Quartz impregnated with ealena, zincblende, clialcopyrite, and 
pyrite, carrying gold and silver. Gangue : quartz and altered 
country rock. 

Palmyra.. 

Locally called trachyte. Decomposed porphyry. Vein: strike, 

Argentiferous galena, with barite and stibnite. Gangue : quartz 


N. 35° W., dip, 65° NE. ; width, 4 feet. 

and altered country. 

Pandora & Oriental. 

Greenish undeterminable rock, locally called trachyte. Vein: 
strike, N. 72° E. ; dip, 60° S. ; width, 10 feet. 

Auriferous quartz, with pyrite and ehalcopyrite. 

Smuggler. 

Greenish undeterminable breccia, locally called trachyte. Vein : 
strike, N. 18° W. ; dip, 65° W. ; width] 10 feet. 

Native silver, stephanite, argentiferous galena, and zincblende. 
Gangue : quartz and altered country. 

Summit. 

Undeterminable eruptice rock locally called trachyte. Vein : 
strike, NE. ; dip, 75° NW. ; width, 4'feet. | 

Argentiferous galena, cerussite, with stephanite and freibergite. 
Gangue : quartz and altered country. 

IRON SPRING DISTRICT. 



Montezuma. 

Crystalline quartz-porphyry. Vein: strike, E. and W. ; dip, 55° 

Galena, cerussite, with some chalcopvrite, in quartz and altered 

. 

S. ; width, 4£ feet. 

country lock. 

Nettie . 

White “siliceous limestone”. (Porphyry?) Vein: strike, NW. j 
dip, 65° NE. ; width, 4£ feet. 

Galena, pyrite, and auriferous iron-stained quartz. 

Nevada . 

Called trachyte. No specimen. Vein vertical; strike, NE. 

Galena, freibergite, ehalcopyrite, and pyrite. Gangue: quartz 
and porphyry. 

Osceola. 

Biotite-poiphyrite. Vein: strike, N. 88° W. ; dip, 70° N. ; width, 

4 feet. 

Iron-stained auriferous quartz. Gangue: quartz and altered 
country. 

Parson. 

Fine-grained very crystalline quartz-porphyry. Vein : strike, E. 
and W. ; dip, 60 N. ; width, 5 feet. 

Argentiferous galena, zincblende, pyrite, and barite. Gangue: 
quartz and altered country. 

Pike . 

Syenite or diorite (?) with a little quartz. Vein: strike, N. 15° 
‘E. ; dip, 75° AV. ; width, 4 feet. 

Argentiferous galena and pyrite, with a little gold, in gangue of 
dolomite aud quartz. 

Valiev View . 

Called trachyte. No specimen. Vein, vertical ; strike, NE. ; dip, 
90° ; width', 3 feet. 

Argentiferous galena and cerussite. 

What Cheer. 

Quartz-porphyry, like Lincoln porphyry. Vein, vertical; strike, 

Argentiferous galeua and freibergite, with ehalcopyrite, pvrite. 

| 

N. 40° E.; width, 4 feet. 

and zincblende. Gangue: quartz and altered country. 


LA PLATA COUNTY. 

La Plata county lies to the south of Ouray and San Juan counties, and is largely a mesa country formed of 
approximately horizontal Mesozoic beds, protruding through which are the eruptive masses of the La Plata 
mountains and the Sierra el Late. The coal horizons underlie a large portion of the county, as well as a portion of 
western Ouray, and developments have been made in the more thickly settled portions. 

In the census year its mines were mostly in the condition of prospects. A schedule was obtained from only 
one producing mine, the Comstock, in the California district, on the west side of the La Plata river, and miles 
north of Parrott City. Its ore deposit occurs in a dike of felsite-porphyry included in a reddish sandstone or quartzite, 
lithologically resembling those of the Upper Carboniferous of Park county. The deposit strikes north and south 
with the formation, dipping G5° to the eastward, and is apparently an impregnation or alteration of the country 
rock for about 6 feet in width near the hanging wall of the dike. Its ore is auriferous pyrite in a quartz gangue, 
with scattered spots of galena and gray copper. Specimens have been brought in from an extremely interesting 
deposit of copper •glance in a coarse conglomerate resembling lithologically those which occur in the lower portion 
of the Triassic formation found to the west of Durango. A similar deposit is said to occur in the valley of the Rio 
Dolores, in the immediate neighborhood of a mass of eruptive rock which traverses the sedimentary conglomerate. 















































86 


PRECIOUS METALS. 


HINSDALE COUNTY. 

Hinsdale county lies to the east of Ouray and San Juan counties, its area being mainly covered by eruptive 
locks, with some exposures of underlying Archaean in the valleys tributary to the Lake fork of Gunnison river. 
Its mines occur mostly between Lake City and the crest of the range which divides this county from San Juan. 
In manner of occurrence of country rock and minerals they resemble those of the latter. Exceptionally, the country 
jock of the Ohio Consolidated mine, on Henson creek, 15 miles west of Lake City, is a fresh feldspar-basalt, 
containing olivine, which is largely altered to serpentine. 


Mine. 


Country rock and vein. 


Ore and gangue. 


OAI.KXA DISTRICT. 

California. Porpliyrite (?) Hanging wall resembles decomposed felsite-por- Argentiferous galenn, freibergite, zincblende. cbalcopyrite, wiUi 

pnyry. Vein: strike X. 57° E.: dip. 55° XW.: banded struc- calcite and rhodoebrosite (?) in quartz gangue. 
ture, 4 feet wide. 

Ocean Wave. Gray eruptive, called trachyte. Vein: strike HE.; dip. 80° S.; Argentiferous galena and freibergite; little native copper. 

width, 4 feet. Gangue: quartz and altered country. 

Ohio Consolidated. j Foot wall fresh feldspar-basalt, with olivine altered to seipen- Freibergite and cbalcopyrite. Gangue: quartz and altered coun¬ 

tine; hanging wall much altered basic rock, possibly the try. 
same. Vein : strike X. 5° W.; dip, 73° W. ; 3& feet wide. 

Palmetto. Gray diabase-porphyrite, with tendency to atuygdaloidal struc- Chalcopyrite, stepbanite, and ruby silver, with some gold in 

ture. Vein: strilie X. 25° E.; dip, 73° S.; 4 feet wide. quartz gangue. 

Silver Cord Extension. Xo specimen; locally called porphyry. Vein: strike X. 10° W.; Freibergite, with native silver and galena, chalcopyrite and zinc- 

dip, 85° E. Xo foot wall found. blende. Gangue: quartz, with a little altered country. 

Decomposed undeterminable rock, locally called trachyte. Vein: Freibergite, galena, and chalcopyrite; quartz gangue. 
strike XE.; dip, 74° (?). 

Decomposed light-colored orthoclase rock, with little quartz ; lo- Argentiferous galena, freibergite, zincblende, and auriferous 
eally called trachyte. Vein: strike X. 55° E.; dip. 62° S.; chalcopyrite; quartz gangue. 
width, 18 inches. 

Xo specimen; called diorite. Vein vertical: strike X. 34° E.... Stephanite and galena, with pvrite and chalcopyrite; quartz 

gangue. 


iTlay & Ute. 

TAKE DISTRICT. 
Hello of the West. 

PARK DISTRICT. 
Inez. 


SAGUACHE COUNTY. 

Saguache county comprises the head of San Luis valley, with the slopes of the Sangre de Cristo range, which 
face it on the northeast, and the Cochetopa hills on the northwest, a volcanic mass, reaching from the southern 
end of the Sawatch range to the San Juan mountains. 

No working mines of the precious metals are reported for the census year. On the western slope of the Sangre 
de Cristo, not far from Hatden’s pass, occurs a rich deposit of red hematite iron ore in limestone (Carboniferous?), 
which is worked by the Colorado Coal and Iron Company, and to which a branch road has been extended from 
the Denver and Eio Grande railroad above Poncho Springs. Iron ore is also said to occur on the west slopes of the 
Cochetopa hills, in the valley of one of the creeks tributary to the Gunnison river. 


RIO GRANDE COUNTY. 

Rio Grande county comprises the very uppermost portion of the valley of the Rio Grande and the eastern end 
of the San Juan mountains, which is made up almost entirely of eruptive rocks, said to belong to the Tertiary 
voles nies. 

Little Annie mine, in the Summit mining district, is the most important producing mine. It is situated about 
28 miles to the southward of Del Norte, at the head of Alamosa creek. It is an exceptionally rich deposit of free 
gold in quartz 45 feet in width at the surface. The quartz is a peculiarly cellular rock, and the cavities are 
supposed to be those left by the leaching out of feldspar crystals. The country rock is probably an older porphyry. 
This could not be determined for want of a specimen; but it has been suggested, with considerable appearance 
of probability, that the so-called vein is an altered porphyry dike impregnated with mineral. 


GEOLOGICAL SKETCH OF WYOMING. 


The territory of Wyoming lies to the north of Colorado, having a corresponding area as measured by degrees 
of latitude and longitude, but set off 2° of longitude to the westward. 

Although directly in the line of the main Rocky Mountain uplift, the larger portion of its area is a plain or mesa 
countiy. The Colorado range extends a short distance north of the boundary of that state, but with a very much 
diminished elevation. In the northwestern corner of the territory is a considerable mountain area, occupied 
principally by the Wind River, Shoshone,and Rig Horn ranges, which are connected with the northern continuation 
of the Colorado range by low east and west ridges, the Sweetwater and the Seminole mountains. In the extreme 
northeastern portion of the territory a portion of the Black Hills uplift is included within its boundaries. 


































GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


87 


With these exceptions its area consists of broad grassy valleys or Tertiary mesas, which either form arid deserts 
or are covered with a somewhat scanty growth of nutritious grasses. But few large streams arc found in the 
territory, although within its area are some of the sources of the three great river systems of the country, viz, the 
Green or Colorado river, which flows southward through its center; the Snake Fork of the Columbia, which takes 
its rise in the northwestern portions; and the Platte, Cheyenne, Powder, and Wind rivers, important tributaries to 
the great Missouri River system. With the exception, therefore, of narrow strips of alluvial soil in the bottom lands 
of these streams and their tributaries, it is of little value for agricultural purposes. On the other hand, the immense 
stretch of grassy plains available for grazing constitutes its great wealth. 

Our geographical and geological knowledge of the territory is mainly obtained from the reports of the 
Exploration of the Fortieth Parallel, whose field of labor covers a narrow strip along its southern border, and from 
detached notes on-the same field made by the Hayden survey. The last season’s field-work of this survey (in 1878) 
covered a considerable portion of the western and northern areas of the territory, but its results are not yet 
printed, (a) 

General geology.— It is doubtful whether any portion of this territory emerged from the surface of the ocean 
during the Palaeozoic and Mesozoic eras. At the most, land areas, if they existed, were confined to the nbrthwestern 
portion, consisting of what now constitutes the Wind River range, and possibly portions of the adjoining mountain 
areas. The mountains of Colorado find their continuation in a system of submerged reefs and small islands, 
stretching in a direction a little east of north to the Black hills of Dakota, and branching off in a northwesterly and 
westerly direction to connect with the Wind River range. In this area sedimentation, fed by material derived from 
the land areas of Colorado on the south, of Utah and Idaho on the west, and of Montana and the Black hills of 
Dakota on the north and east, went on without any important interruption until the close of the Cretaceous. As 
already noted in Colorado, there was a probable continental elevation toward the close of this period, resulting- 
in the partial inclosure of the basin which forms the central portion of the territory, so that its waters became 
gradually fresher, and were finally shut off from all communication with the ocean. The conditions of this period 
were particularly favorable for the formation of coal, and the upper portion of the Cretaceous, wherever it outcrops 
throughout the territory, has been found to yield an abundance of this valuable mineral. After the great 
dynamic movement at the close of the Cretaceous large areas were still beneath the surface of fresh-water Tertiary 
seas, in which deposition went on with great activity. It is as yet too early to outline definitely the areas of -these 
different seas, but it is known that within the Tertiary system there exist important developments of beds of the 
Eocene, Miocene, and Pliocene periods. The wealth of fossil remains of animals, fishes, and plants which have 
been exhumed from these beds has already given them a world-wide renown among students of the evolution of life 
on the globe. 

The surface changes during the Quaternary have been comparatively small as compared with those of the 
mountain regions adjoining; and yet enormous masses of the beds deposited in the Tertiary era have been swept 
away. In the Wind River mountains a local system of glaciers existed relatively greater even than those of 
Colorado, living relics of which are said still to exist in the higher parts of the mountains. Of eruptive rocks there 
seems to be a singularly small development iu this great area. As far as known, they are mainly confined to the 
Yellowstone park, in the extreme northwestern portion of the territory, whose geysers, generally considered as 
intimately connected with recent volcanic action, eclipse the hitherto unrivaled springs of the volcanic island of 
Iceland. In the midst of the Tertiary plains of the great Green River basin is found a small flow of leucite-lava, the 
only occurrence of this mineral, which is characteristic of the lavas of Vesuvius, hitherto discovered on the American 
continent. It is not to be wondered at that we have but little information about earlier eruptive rocks, since so 
much of the area of the country is covered by sediments deposited since their eruption and the Arch man areas in 
which they might be found are as yet comparatively unstudied. 

Gold and silver.— As might be inferred from the above brief sketch of its geological structure, Wyoming 
can scarcely rival its northern and southern neighbors as a producer of the precious metals. Its actual resources 
have as yet, however, been scarcely developed, partly because the broad plain areas offer little inducement to the 
prospector, and partly because he has hitherto been debarred from the northern mountain areas by the Indian tribes 
to whose reservation they belonged. The only discoveries of ores of these metals which are known to the writer are 
confined to the Medicine Bow range, a northern offshoot of the Colorado range, to the south of the Laramie plains; 
to the Sweetwater and Seminole mountains, a group of hills running east and west from the northern end of the 
Laramie hills to the Wind River mountains; and to the mining districts near South Pass, at the southeastern end of 
the Wind River mountains. From the latter reg'on alone were returns obtained by the census experts. 

The Archman nucleus of the Wind River mountains consists mainly of granite, on whose northeastern flanks 
rest the Palmozoic and Mesozoic formations; while on the southwest the Tertiary beds of the Green River basin 
come directly in contact with it. At the southeastern extremity of the rauge the granites give way to a series of 
schistose rocks, prevailingly gneiss and mica-schist, whose area extends out for some distance beyond the actual 


a The writer lifts been favored with a glance at the topographical and geological maps of this leport, from which part of the data 
herein contained are derived. 






88 


PRECIOUS METALS. 


mountain uplift. In the foot-hills of the range, near the South pass, are the California, Miner’s Delight, and Shoshone 
districts, the former near Atlantic City, and the latter near South Pass City. Mines were first discovered here in 
the fall of ISG7, and the region was the scene of considerable excitement in the following year. Wild cat speculation, 
danger from the Indians, and other causes have combined to prevent its proper development; so that, although the 
mines are now almost deserted, it would seem that their abandonment has not been necessarily due to want of 
good ores. From the data obtained, they seem to be mainly free-milling gold ores, occurring either in quartz veins or 
as impregnations of the country rock, which is mainly gneiss of both micaceous and hornblendic varieties. It 
is difficult to form a clear idea of the exact geological relations of the deposits, but they would seem to be in some 
respects analogous to those of the Black hills. Galena and copper ores are also said to have been found in the 
vicinity, but their exact location is not given. 

Copper ores have recently been developed near the Platte river to the northwest of Fort Laramie. From 
the boundary of Colorado northward to the Platte river extends a broad flat ridge, known as the Laramie hills, 
whose surface is made up of Archman rocks, from which the Palmozoic and Mesozoic beds, which originally covered 
it, have been removed by erosion. From Laramie peak, the northern extremity of this ridge, which itself was 
possibly an island in the Cambrian ocean, an irregular reef of Arcliman rocks extended in a direction a little 
north of east toward the Black hills. Portions of this reef, which in Tertiary times projected above the water, 
now form an irregular group of hills, known as the Rawhide buttes. At the southern base of these hills, in the 
sedimentary rocks which rest against the Archman, occur the deposits of copper above mentioned. The ore consists 
of carbonates, oxides, and silicates of copper, containing no silver, and, thus far, not sufficient sulphur to make a 
matte. . To what geological horizon the country rock inclosing these ores belongs is not known, nor the character 
of the deposits ; but it seems probable that they are rather impregnations of a certain bed than a vein crossing the 
stratification. 

Coal and iron.— The actual development of coal in Wyoming is already very considerable, and its possibilities 
are immense. With the exception of the mountain ridges, the entire area of the territory may be said to be underlaid 
by the coal formation. Over a very great portion of this area, it is true, this formation is so deeply buried beneath 
Tertiary deposits that it is practically unavailable. On the other hand, the coal formations are by no means 
absolutely horizontal over all the plain country, but have been brought to the surface by various geological movements, 
so that the actually known extent of its outcrops is very great. The two largest basins are those of the Laramie 
plains and of the Green River basin. In the former coal is worked extensively at Carbon, on the Union Pacific railroad; 
in the latter, coal beds have been opened at Black Buttes and Point of Rocks, on the east, and at Rock Springs, 
on the west of a synclinal basin lying east of Green river, while the outcrops of a second basin to the west of 
Green river have been found extending all along the western borders of the territory and beyond the line in Utah 
from near the head of Bear river, following the valley of that stream and of the south fork of Snake river as far as 
the junction of the latter with Henry’s fork, a distance, in round numbers, of 175 miles. Outcrops have also been 
found extending around the northwestern point of Wind River range, at the head of Gros Ventre and Wind rivers, 
and at various points among the bays of the Big Horn mountains and the Black hills of Dakota. They have also 
been found not far from the copper mines to the north of Laramie peak. The only actual working mines, however, 
are those along the line of the Union Pacific railroad, which are either owned by or are indirectly under the control 
of that corporation. Iron ore has been discovered in immense masses in the Laramie hills at the head of Horse 
creek. This ore is magnetic. The specimens as yet tested have proved to contain too large a percentage of titanium 
to be of marketable value, but it is by no means certain that a more careful investigation may not discover beds 
comparatively free from this injurious constituent. A valuable deposit of remarkably pure red hematite also exists 
in the Carboniferous strata resting against Rawlings peak. The ore was used for some time as a mineral paint, but 
the mine has of late years for some unknown reason been abandoned. Petroleum is found in the rocks of the 
Cretaceous formation at many points, and oil of excellent quality for lubricating purposes has been obtained in small 
quantities; but the practical value of this formation as an oil producer has not yet been thoroughly tested. At 
various points in the Tertiary plains are beds of dried-up lakes containing valuable deposits of alkaline salts. These 
are specially frequent to the north of the Union Pacific railroad, between the Platte and Green rivers, and in 
one case a deposit of solid sulphate of soda 15 feet in thickness has been proved. Their actual development is 
awaiting the advent of some enterprising manufacturing chemist. 


GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


89 


SWEETWATER COUNTY. 


Mine. 


CALIFORNIA DISTRICT. 


Country rock and vein. 


American. 

Buckeye State. 

Caribou. 

Manchester. 

Mary Ellen. 

Victoria. 

mixers’ delight district. 


Fine-grained gneiss. Vein: strike, HE. ; dip, S.; 2 to 8 feet wide. 

Hornblende-gneiss. Vein: strike, E. and W.; dip. H.; width 
irregular, 8 inches to 12 feet. 

Areluean schists. Vein: strike, HE.; dip, H.; width irregular, 
8 inches to 5 feet. 

Amphibolite and gneiss. Vein: strike,NW.; dip, 45 3 S.; width 
irregular, 4 to 16 feet. 

“Black granite ” ; no specimens ; probably gneiss. Vein: strike, 
HE.; dip, W ; average 1 foot thick. Irregular on hanging wall. 

Gneiss. Vein : strike, HE.; dip SE.; 1 to 4 feet wide. 


Free gold in quartz. 
Do. 

Gold-bearing quartz. 
Do. 

Free gold. 

Do. 


Ore and gangue. 


Hartley.. 

Miners’ Delight 
Sidney Johnston 
Yellow Jacket... 


Compact dark gneiss. Vein : strike, SW.; dip, S.; 6 inches to 2 
feet in width. 

Fine-grained gneiss. Vein : strike, HE.; dip, S.; 1 to 6 feet in 
width. 

Gneiss and schists. Vein : strike, HE. ; dip, S.; width, 6 inches 
to 5 feet in width. 

Gneiss and schists. Vein : strike, HW.; dip, S.; 1 to 4 feet in 
width. 


Free gold in quartz and decomposed country. 
Free gold, with little silver in quartz. 

Free gold in quartz. 

Do. t 


SHOSHONE DISTRICT. 

Cariso. 


Apparently Archaean gneiss. Vein: strike. H.W. ; dip, S. ; 2 to 
8 feet wide. 


Do. 


GEOLOGICAL SKETCH OF THE BLACK HILLS OF DAKOTA, (a) 

The Black hills of Dakota constitute a wooded island rising from 2,000 to 3,000 feet above the treeless plains 
of Dakota, quite isolated from the main chain of the Rocky mountains, whose foot-hills lie 100 miles further to the 
west. Their uplift forms an oval some 120 miles in length by 50 in extreme width, its longer axis having a direction 
a little to the west of north. The surrounding plain or mesa country is covered by practically horizontal beds of 
Cretaceous and overlying Tertiary formations. 

Their geological structure is that of a singularly regular quaquaversal having a central nucleus of Areluean 
schists, on which rest beds of the Palteozoic and Mesozoic formations dipping away from it in every direction, 
the outcrops of the latter forming a series of fringing reefs, or so-called hog back ridges, which completely encircle 
the island. The area in which the Archaean rocks are exposed occupies the eastern and higher portion of the hills, 
and also forms an oval some 5G miles in length and 24 in extreme width, its longer axis running north and south. 
The northwestern portion of the hills is covered by nearly horizontal beds of the Palaeozoic formation, patches of 
which are still left in the Archaean area, while the steeper dips of the quaquaversal are found as a rule only near 
the foot-hills. 

The Archaean rocks of the Black hills are divided by Mr. Newton into two series, an older and a newer 
Archaean, the former, in general, occupying the southwestern portion of the oval area above mentioned, and the 
latter (the newer Archaean) the northeastern portion. The latter ho considers to closely resemble the Huronian 
of the east, and it is certainly unlike any Archaean formation yet studied in the Rocky mountains, except that 
of the Red Creek area in Wyoming, (0) which was also considered as corresponding to the eastern Huronian, 
and resembles it lithologically. The older Archaean is also somewhat different from that of Colorado, in that it 
contains but little gneiss. The granite which occurs in it, however, would not seem to form so much of a 
distinctive character from this Archaean as was thought by Mr. Newton, since it is apparently an exaggerated form 
of the pegmatite, which is largely developed in Colorado in secondary veins and irregular masses traversing the 
gneiss and schists. This older Archaean consists, according to Mr. Newton, of quartzose, garnetiferous, and 
ferruginous mica-schists, chloritic schists, amphibolites, and subordinate gneiss, with interlaminated veins of quartz 
carrying gold. In these occur large masses of granite of lenticular shape, conforming in general with the 
stratification of the schists, and made up of very large individuals of quartz, feldspar, and mica, crystalline in . 
structure, but not always in complete crystals. Tourmaline crystals are quite common in the granite. This 
granite Mr. Newton regards, from the fact that it sometimes incloses fragments of schist and has polished contact 
surfaces, as distinctly of an eruptive origin, but as erupted in pre Cambrian times. The rocks of the newer Archaean 
are, according to him, not essentially different in mineralogical composition, but are characterized by a much finer 
texture. They consist of micaceous clay slates, siliceous slates, hydro-mica schists, and quartzite. Quartzite forms 
an important constituent, often carries a certain amount of mica, and occurs in powerful beds from 50 to 200 
and sometimes 500 feet thick. The mica-schists are often garnetiferous, and contain also staurotide crystals. 

a Tlic data for this sketch, additional to that gathered by census experts, were obtaiued from A Report on the Geology and Resources 
of the Black Bills of Dakota, by Henry Newton and Walter P. Jenuey, observations made in 1875 and published in 1880, and from a paper 
by W. B. Devereux on “ The occurrence of gold in the Potsdam formation”, Trans. A. I. M. E., February, 188*2. 

b Geological Exploration of the Fortieth Parallel, vol. II, Descriptive Geology, page^GO. 





































90 


PRECIOUS METALS. 


Gneiss also occurs, but rarely. To these should be added, from data furnished by the census specimens, a series 
of very line phyllites and some actinolite schists. Interlaminated lens-shaped bodies of quartz are also noted 
in this series by Mr. Newton, and are by him supposed to be auriferous. Mr. Jenney considers these quartz bodies 
as differing in the two series, though the reasons for this difference are not apparent. Both are parallel with that 
bedding, and neither traverses it; both carry gold, but those in the older series he considers interlaminated fissure 
veins and continuous, and those in the newer series as segregated veins and not continuous. The enormous quartz 
bodies which have yielded the principal gold product of this region belong to the latter class. 

Overlying unconformably these Archaean schists is a thickness, in round numbers, of 2,500 feet of Palaeozoic 
and Mesozoic beds, which, according to Mr. Newton, are entirely conformable within themselves. These consist 
first of a thickness of 250 feet of calcareous sandstones and quartzites, having a conglomerate with calcareous 
cement at or near the base and local developments of glauconite grains in the upper part. In these are found 
well-recognized fossils of the Potsdam formation, which is classed by Mr. Newton as Silurian, but which it is now 
more common to group under the Cambrian epoch. Above the Potsdam sandstones are pinkish and gray limestones, 
passing up by a gradual transition into red and variegated sandstones, in the former of which are found well-recognized 
Carboniferous types. Over these are the red Triassic sandstone beds, succeeded by variegated clays and marls, with 
a little limestone of Jurassic age and coarse yellow sandstone, with clays and shales of the Cretaceous formation. 
The thicknesses given by Mr. Newton are 690 feet for the Carboniferous group and 1,440 feet for the entire 
Mesozoic system. The striking features in this series of deposits are the apparent absence of representatives of 
the formations included between the Cambrian and Carboniferous and the relative thinness of the entire series as 
compared with sections found in other parts of the country. The latter fact is less surprising when it is considered 
that the tendency of the Rocky Mountain deposits has been observed to be a thinning out toward the east, and 
that the Black hills were an island at least 100 miles east of the Archtean shore-line. Whether the apparent gap 
in the series signifies that there was actually a cessation of deposition during Silurian and Devonian times, or 
whether representatives of these formations exist but have not yet been detected, is a question that can only 
be definitely determined by far more detailed studies than have yet been made. 

The geology of the Black hills is of singular interest, not only to the general but to the economic geologist, 
and the facts already obtained show that its history has been a remarkably varied one. According to Mr. Newton, 
there is evidence that the newer Archtean is unconformable to the older; in other words, that dynamic movements 
took place, and land existed here which was acted on by erosion before the close of the Archaean. The conglomerate 
at the base of the Potsdam bears unmistakable evidence of having been a beach or shore formation, and shows 
that new land appeared at the close of the Archaean, while the comparatively horizontal position of the Potsdam 
and Carboniferous beds in elevated portions of the hills seems to indicate a gradual subsidence during the Cambrian, 
which, if the Devonian be really wanting, must have been followed by a sufficient elevation to prevent the sediments 
of that period covering its area. This elevation, however, must have been of such a gradual character that the 
formations were not disturbed, inasmuch as the Carboniferous beds were deposited with perfect conformity on the 
Cambrian. At the close of the Cretaceous the area of the hills was again lifted above the sea and a second 
conglomerate deposited round its shores. Erosion during this time removed a large portion of the Mesozoic and 
Paleozoic beds to form the surrounding Tertiaries; and that elevation has gone on since Tertiary times seems to 
be proved by the evidence of conglomerate beds more recent than the Tertiary, which exist, according to Mr. Jenney, 
300 feet above the present stream beds, and are made up of bowlders of the Archaean and other rocks from the 
interior of the hills. These gravels or conglomerates Mr. Jenney regards as quite distinct from those of the present 
stream-beds, and as probably dating back to the close of the Glacial epoch. There are thus four different ages of 
gravel formations, all of which, except possibly the third, have been proved to be gold-bearing: 

First. The Potsdam conglomerate. 

Second. That at the close of the Tertiary. 

Third. That at the close of the Glacial period. 

Fourth. The recent. 

Of eruptive or igneous rocks, of which there are abundant outbursts, especially in the northern portion of the 
hills, where the richest mineral deposits have hitherto been found, Mr. Newton recognizes only those of Tertiary 
age. It seems probable, however, that had not his untimely death cut short his observations a further study might 
have led him to modify this opinion. Mr. Caswell, to whom the specimens of eruptive rock were submitted for 
microscopical examination, says himself that in several cases he would have classed the rocks as quartz or feldspar- 
porphyries had not their geological relations, as described to him, forbidden it. Among the census specimens are 
some which undoubtedly belong to these types. They are the rocks which are described by Mr. Devereux as 
breaking in dikes through the Potsdam conglomerate and spreading out over its surface in the neighborhood of 
Lead City. Moreover, the structural relations of the eruptive masses which form many of the prominent peaks, 
and which, according to Mr. Newton, have uplifted the surrounding sedimentary beds, belong rather to the type of 
earlier intrusive eruptives, analogous to the laccolitic bodies, than to the Tertiary volcanics, which as a rule have 
flowed out on the surface without exercising any considerable disturbing influence on the sedimentary beds through 
which they have passed. 


GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


91 


To the economic geologist the most interesting fact in the geology of this region is the definite date given to 
the formation of the gold deposits. The Potsdam conglomerate is in places an actual placer deposit formed on the 
beach of the Cambrian ocean from the debris of veins at present worked in the Archiean. The gold of the Black 
hills is therefore distinctly of Arclnean age. Mr. Devereux also recognizes a probable secondary deposition, which 
he considers as probably resulting from chemical solutiou of gold contained in the Potsdam conglomerate and 
rede^osited in the underlying schists. He also seems to consider the deposition of certain silver-bearing ores in the 
neighborhood of Bald mountain, a region traversed by bodies of porphyry in the forms of dikes and sheets, which 
occur in the quartzite adjoining these bodies, as dependent on the eruption of the porphyry. If the section which 
he gives of the region in the neighborhood of Deadwood gulch be correct, the porphyry must be of subsequent 
date to the erosion of the Cretaceous and Palaeozoic rocks, and therefore probably post-Cretaceous. 

Ore deposits. —The most characteristic ores of the Black hills are auriferous pyrites, now almost completely 
oxidized, impregnating lenticular masses of quartz, and portions of the adjoining schist in the newer Archaean of 
Newton. Owing to the decomposed condition of the rock and its freedom from injurious metallic combinations 
these ores are so exceptionally easy of amalgamation in the stamp-mill that they yield a profitable return, even 
when carrying only from $4 to $6 per ton in gold. These deposits have been mainly developed in the extreme 
northern portion of the Archaean area at the head of the Whitewood gulch, in the vicinity of Lead, Central, and 
Deadwood cities. The country rock here consists of fine-grained mica-schists, argillites, or phyllites, with numerous 
interlaminated lenticular bodies of quartz parallel with the stratification, which has a prevailing northwesterly 
strike and a dip of from 50° to 75° to the northeast. The ore belts are from 40 to 200, 300, and even 500 feet 
in width, and consist of impregnations of these quartz masses and portions of the adjoining country rock with 
iron oxide, resulting from the decomposition of pyrites carrying fine gold. In these belts are barren streaks or 
“ horses” of country rock and dikes or bodies of what is locally called porphyry. It is evident that these deposits 
have none of the characteristics of a true fissure vein, though they are none the less valuable on that account. It 
is probable also that the individual ore bodies, or lenses, are of limited extent both horizontally and vertically, or, 
as Mr. Jenney says, not continuous. This fact is not necessarily derogatory to the deposits as a whole, since, while 
one lens may pinch out, another may be found contiguous, though not exactly in the same plane. Moreover, in 
spite of the popular delusion in favor of fissure veins extending to the center of the earth, all known facts go to 
prove that all ore bodies are limited in extent, the difference between one and another being merely in the extent 
of the limit. Horizontally the limit is easily traced, although in depth it is sometimes beyond the present reach 
of practical mine development. 

Another important source of gold is the cement or Potsdam conglomerate, which, though its ore is milled in the 
same manner as the vein material, is in fact an ancient placer deposit. It is only of local extent, is of varying 
thickness, and is made up of rounded and angular fragments of quartz, hematite, and Arclnean schists, often 
with ferruginous cement, and, according to Mr. Devereux, carries free gold, distributed in an exactly analogous 
manner to that found in modern placers. In many cases the cement deposit is worked as a horizontal vein, while a 
vertical vein is described as occurring immediately beneath it. Whether Mr. Devereux would consider all these 
vertical veins as instances of later deposition is not known to the writer. 

In mines reported from the Bald Mountain district, at the head of the Whitewood gulch, the reports show a 
different class of deposits, which consist of chlorides of silver and iron oxide, carrying gold, impregnating thequar tzite 
strata to a thickness of several feet. These are probably the deposits which Mr. Devereux considers as a later 
formation, and connected with the porphyry outbreaks. No specimens of porphyry were returned by experts, but 
the district is apparently in the neighborhood of Terry’s peak, the rock of which Mr. Caswell reports as a granitic 
rhyolite, with a completely crystalline groundmass, closely resembling granite- or felsite-porphyry. 

In the Bear Butte district, 10 or 12 miles to the east of Deadwood, irregular deposits of argentiferous galena 
and cerussite, with oxides of iron carrying both gold and silver, occur in limestones and quartzites, sometimes 
parallel to the stratification, and again crossing it. Gold is also obtained from a conglomerate or breccia largely 
made up of fragments of what is apparently felsite porphyry. The geological relations of this class of deposits 
are not clear. 

In Pennington county, in the central portion of the bills, free-milling gold ore is found in Archaean rocks m the 
Rockford, Cross, and Newton Forks districts; and to judge from the specimens of country rock sent in they occur 
apparently in the same Archaean formation as that of the Whitewood district, although, according to Mr. Newton’s map, 
a portion at least of these mines would be included in the older series. It is to be noted, however, that the geological 
outlines of the map are confessedly imperfect, owing to the fact that Mr. Newton’s material had to be worked up 
by another hand than his own. In the Cross district the ore-body seems to be the impregnation of a mass of 
actinolite-biotite schist, instead of quartz, included within the mica-schist country rock. It is to be noted, however, 
that in these districts, while, according to the census schedules, the formation strikes nearly north and south, its 
dip in the Rockford and Cross districts is to the eastward, and in the Newton Forks district to the west. 

In Custer county, still farther south, are the Cole and Custer districts, in which the same lenticular masses of 
quartz, carrying free gold, occur in mica-schists. Both these districts are included in Newton’s older Archaean area. 
The specimens of country rock sent in are micaceous schists, carrying considerable quartz, and sometimes 


92 


PRECIOUS METALS. 


garnetiferous, while the ore-bodies, in addition to the quartz, are sometimes amphibole-schists, and in one case 
consist entirely of fibrous tremolite. Associated with the gold is frequently a little silver. The prevailing strike 
is here also nearly north and south, and the dip to the westward. 

Three miles to the northwest of Custer City is a mica mine, in one of the bodies of granite described 
by Mr. Newton. In its general character it resembles the pegmatites of. Colorado, but the size of the individual 
constituents is actually gigantic, and the association of minerals is somewhat remarkable. The data are not 
sufficient to determine the exact geological relations of the rocks. The foot wall of mica-schist strikes north and 
south, and dips 40° to the westward. Above this a thickness of four feet is worked for mica, which occurs in large ■ 
sheets over a foot in diameter, usually nearly perpendicular to the foot wall. Specimens from the zone next above 
the mica show albite (var. cievelandite), labradorite, beryl in crystals 2 to 3 inches in diameter, and a lithia-mica 
in small leaves. Above this is pure milky quartz of great thickness, said to extend to the top of the hill, over 
100 feet above the vein. Whether these deposits* prove of economic value or not, a visit to it would evidently be 
fruitful in interesting results to the mineralogist. 

Placer deposits. —The placer deposits of the Black hills are apparently of great extent and richness; but, 
except those immediately adjoining the beds of the present streams, which are largely worked out, they have as yet 
proved of little practical value, owing to the difficulty of ptocuring a sufficient supply of water. As already stated, 
Mr. Jenney makes four different ages of gravel deposits. The earliest, or Potsdam conglomerate, is worked as a 
deep mine, and its ore is regularly crushed in the stamp-mills. Of the pre-Tertiary conglomerate no data are 
available as to its contents in gold. It occurs, according to Jenney, under the Miocene beds at the mouths of 
Spring and Rapid creeks, forming a bed 6 feet in thickness, made up of bowlders of granite, trachyte, slate, 
quartzite, and quartz. Mr. Jenney says the glacial deposit which occurs sometimes 300 feet above the present bed 
of the creek has been proved to be rich by actual test, but cannot be worked, owing to the want of a sufficient 
head of water. The recent deposits of the present canons, according to data furnished by the census, have been 
worked principally in the Arch man area, and have an average depth of from 4 to 30 feet. Mr. Devereux gives some 
interesting facts concerning the placer deposits of Deadwood and its tributary gulches. According to him, these 
are formed in part from the disintegration of the Potsdam conglomerate bed and in part from the actual wearing 
away of the quai'tz deposits in the Archman, which accounts for their exceeding richness; the placers of 
Black Tail gulch were entirely derived from the disintegration of the cement, as the Archman, at the head of the 
gulch, has not been exposed to erosion in recent times. To account for the known superior fineness of placer gold 
over that in veins, he assumes that the chemical agencies to which the gold has been subjected since it was liberated 
from the vein have acted more energetically on the silver than on the gold. To prove this he shows from actual 
figures that while the average fineness of the gold from five different veins was 0.830, gold from the placers, which 
would have resulted from the disintegration of these veins, averaged about 0.900, and that the small, thin pieces 
of gold, which had proportionately greater surfaces than the coarser particles, were finer than the latter. 

The other minerals of economic importance found in the Black Hills region are beds of gypsum, which occur 
in the Triassic formation, and of coal, which is mined in the Cretaceous beds to the northwest of the hills. 


LAWRENCE COUNTY. 


Mine. 


Country rock and remarks. 


Ore and gangue. 


WHITE WOO I) DISTRICT. 


Badger . 

Black Tail. 

Caledonia. 

Champion. 

Dead wood-Terra. 

Esmeralda. 

Fairview. 

Father De Smet . 
Flora Bell_ . 

Giant & Old Abe 
Goldfinch. 


Hanging wall felsitic rock with stratified appearance, probably 
eruptive. Foot wall mica-schist, with some chlorite. Ore belt 
vertical. Strike, NW., 200 feet wide; capped by conglomerate. 

Conglomerate (cement deposit) of fragments of Aichman schist. 
Compact felsite overlying conglomerate. Ore body, horizontal, 
14 feet thick. 

Hanging wall phyllite, with pyrite and garnet. Foot wall mica- 
scliist with ebloritic layers. A felsite occurs whose relation is 
not clear. Strike, X'. 5° W.; dip, 51° E. (?); twoorebelts, oue40 
feet, the other 182 feet wide. 

Cap and hanging wall felsite-porphyry. Foot wall calcareous 
qnartzite. Horses in vertical part of vein composed of car 
bonates of iron, lime, etc. Strike of formation, XE.: dip, 75° E.; 
ore belt, 35 feet wide. 

Hanging wall chlorite-schist with garnet. Foot wall mica-slate 
formation. Strike, XW.; dip, 50° to 75° XE. 

Probably Archaean. Xo specimens. Overlaid by conglomerate 
(cement), i 

Archman overlaid by conglomerate. Strike, XW.; dip, 50° to 
75° XE.; cement, 20 feet thick; ore belt, 200 feet wide ,- felsite 
((), above the conglomerate. 

Chloritic schists. Strike, XW.; dip, 50° to 75° XE.; ore belt, 
150 feet wide, with horses of barren rock. 

Phyllite on hanging wall. Altered schist on foot wall. Horizon- 
1 till conglomerate capped by felsite (?) above. Strike, XE. ; dip, 
85° W. 

Archman schists impregnated with iron. Strike, XW.; dip, 
50° to 75° XE.; ore belt, 60 feet. wide. 

Quartz conglomerate, overlaid by fine-grained Potsdam sand¬ 
stone; quartzite (?) below. 


Free-milling auriferous quartz. 


Free gold in conglomerate. 


Pyritiferous chloritic schists carrying gold. Chlorite apparently 
comes from actinolite. 


In part steeply inclined beds, in part horizontal beds resting on 
upturned edges of Archman, overlaid by porphyry. 


Ferruginous quartz carrying" gold and a little silver scattered 
through a belt of Archman, 250 feet wide. 

Free gold in horizontal cement deposit, and segregated quartz 
lenses in schists below. 

Gold-bearing cement and quartz lenses in iron-stained mica- 
schist. 


Quartz lenses and altered schists, with pyrite ; gold-bearing. 


Gold-bearing cement and schist impregnated with quartz. 


Ferruginous gold,-bearing quartz, with a little pyrite, impregnat¬ 
ing schists. 

Cement 5 to 6 feet thick, carrying free gold. 




/ 
























GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


93 


LAWRENCE COUNTY—Continued. 


Mine. 

Country rock and remarks. 

Ore and gangue. 

WIUTKWOOD district— cont’d. 


• 

Golden Gate. 

Fine grained mica-schists. Stiike, NW.; dip, 50° to 75° NE.; ore 
belt, 25 feet wide. 

Quartz and schists, with little pyrite ; gold-bearing. 

Golden Terra. 

Mica-slate on hanging wall. Mica-schist, rich in quartz and mi¬ 
croscopic ore grains, on foot wall. Strike, N¥.; dip, 50° to 75° 
NE. ; ore belt 300 feet wide, with “ porphyry ” dikes and horses 
of slate. 

Ferruginous quartz, with little pyrite in slate. 

Gopher. 

Fine-grained compact mica-schist- Strike, NW.; dip, 50° to 75° 
NE.; ore belt 00 feet wide. 

Lenses of quartz and decomposed schists; gold-bearing, with 
little pyrite. 

Great Eastern. 

Conglomerate of quartz and some schist, overlaid by quartz-por¬ 
phyry. Dip, 15° E.; 3 feet thick ; resting on schists. 

Free gold in cement. 

Hidden Treasure. 

Conglomerate of quartz and schist fragments ; horizontal. Thick¬ 
ness, 20 feet to nil. Felsite above, Archman below. 

Free gold in cement. 

Highland. 

Archaean schists. Argillite on foot wall; lenticular bodies of fel¬ 
site (?) parallel with the formation. Strike, N W.; dip, 50° to 75° 
NE.; ore belt 550 feet wide, less felsite bodies. 

Ferruginous quartz and schist, with little pyrite; gold-bearing. 

High Lode. 

Conglomerate, resting on fine-grained Archasan schists, overlaid 
by Potsdam sandstone. Horizontal; 8 feet thick. 

Free gold in cement. 

Homestake. 

Arcliajun schists and porphyry (?) bodies. Strike, N. 10° to 38° 
W.; dip, 51° E.; ore belt 40 feet wide. 

Ferruginous quartz and ^phist, with little pyrite, carrying free 
gold. 

Louella. 

Conglomerate, resting on Archie an, overlaid by sandstone. Dip, 
30° E.; 7 feet thick. 

Free gold in cement. 

Oi o Cash. 

Felsite-porphyry. Strike, NW.; dip, 30° NE.; ore belt 150 feet 
wide. 

Gold-bearing hematite and limonite in quartz. 

I’ecclio. 

Conglomerate, capped by felsite and resting on Archaean schists. 
Strike of latter, N. 5° W. 

Free gold in cement, and gold-bearing quartz and schists in 
Archatan. 

Portland..... 

Quartzitic sandstone (Potsdam?). Strike, NW.; dip, 8° SW.; 
deposit, a nearly horizontal bed and a vertical vein below. Hor¬ 
izontal vein, 7 feet thick; vertical; strike SW., 5 feet thick. 

Quartzite, impregnated with hom-silver, iron oxide, and some 
gold. 

Rattler. 

Hanging wall quartzite-schist, foot wall mica-schist. Strike, 
N W.; dip, 75° NE.; 40 feet wide. 

Ferruginous gold-bearing quartz. 

Scandinavian. 

Archaean schists. Ore belt 38feet wide; strike, NE.; dip, 85° N W. 

Quartzose iron-stained masses, carrying gold. 

Sir Roderick Dhu. 

Chloritic schists and mica-slates. Ore, lenticular mass ; dip, 85° 
NW. 

Lenses of quartz and pyrite, carrying gold. 

Snowstorm. 

Fine-grained calcareous sandstono above, quartzitic schist below. 
Deposit, horizontal: 3 feet thick. 

Quartzose mass, impregnated with gold and chloride of silver. 

BEAU BUTTE DISTRICT. 



Carter. 

Mica-schist, with needles of decomposed hornblende. Strike, 
NW.; dip, 85° W.; ore belt, 100 feet wide. 

Lenses of quartz, impregnated with oxide of iron, and carrying 
gold. 

Clermont. 

Fossiliferous limestono on hanging wall. Fein vertical; strike, 
NE.; 40 feet wide. 

Siliceous hematite, quartz, chalcedony, ocher, and in part earthy 
limestono, carrying gold and silver.' 

El Refugio .,. 

Quartzite. Strike, NE.; dip. 15° SE. Ore bodies irregular, follow- 

Gold- and silver-hearing galena, altered to cerussite; crystals of 

ing stratification ; average, 2 feet thick. 

pyromorphite and wuitenite. 

Escondido. 

Earthv limestone. Deposit : dip, 80° E.; 5 feet wide. 

Galena, pyrite, and zincblende, carrying silver. 

Florence. 

Ferruginous quartzite (Potsdam?). Horizontal; irregular bodies 
following stratification ; 2J feet thick. 

Pyrolusito, ocher, and siliceous hematite impreguatingquartzite, 
carrying silver. 

Hoodoo. 

Conglomerate of felsite and stratified rocks; explored to a depth 
of 25 feet. 

Free gold in conglomerate. 

Keystone. 

Porphyry, with little quartz large pink orthoclase crystals ; no 
mica or hornblende; called “ porpliyritic conglomerate”. 

Quartz-bearing porphyry, impregnated with auriferous pyrites. 

Merritt No. 2. 

Quartzite (Potsdam). Dip, 35° E.; deposit, 7 feet thick. 

Argentiferous galena, limonite, and ocher, with little gold. 


Conglomerate of schist fragments, with ferruginous cement. 

Free gold in cement. 

Free gold in conglomerate, with ferruginous cement. 

Rich. 

Breccia, or conglomerate of porphyry fragments. Dip, S. and E . 

Sitting Bull. 

Quartzite (Potsdam). Dip, 20° SE.; deposit, irregular bodies fol¬ 
lowing stratification. 

Galena and siliceous hematite, with carbonate, carrying gold and 
silver. 


Conglomerate or breccia of felsite-porphvry. 

Country rock, stained with oxide of iron, and carrying gold. 
Galena, carrying gold and silver. 

Washington. 

Quartzite (Potsdam). Deposit, irregular following stratification; 
horizontal, 1 to 8 feet thick. 

Fellow Jacket. 

Foot wall, mica-schist; hanging wall, indistinctly schistose rock. 
Strike, N W.; dip, 20° SW.; ore body 3 feet thick following the 
formation. 

Cerussite, carrying silver and some gold in quartzose mass. 


PENNINGTON COUNTY. 


ROCKFORD DISTRICT. 



Alta. 

•Hanging wall greenish decomposed mica-schist. Foot wall dark 
ph\ llite. Sti ike, N.; dip, 45° E.; ore belt, 100 feet wide. 

Quartz and altered schist, carrying free gold. 



Decomposed schist and quartz, carrying free gold. 

Altered country rock, carrying free gold. 

Evangeline. 

Siliceous schists. Strike, N. and S.; dip, 17° E.; ore belt, 40 feet 
wide. 

CROSS DISTRICT. 




Mica-schist. Strike, N. 17° W.: dip, 85° E.; ore belt, lOOfeetwidc. 

Actinolite-biotite schist, carrying gold and silver. 

Quincy and Little Grace. 

Siliceous mica-schist. Strike, N. 18° W.; dip, 85° E.; ore belt, 

Do. 


90 feet wide. 


NEWTON FORKS DISTRICT. 



King Solomon. 

Light-colored phvllites, garuetiferonson foot wall. Strike, N. 15° 
W. ; dip, 86° W. 

Quartz and country rock, carrying gold and silver. 

Queen Bee. 

Fine-grained mica-schist. Strike, N. and S.; dip, 45° W.; ore 
belt 1C feet wide. 

Quartz and country rock, carrying free gold. 

Royal Bengal Tiger. 

No specimen ; apparently same as abovemine. Strike, N. audS.: 

Quartz and schists, carrying free gold. 


dip, 85° W.; ore belt 10 feet wide. 









































































94 


PRECIOUS METALS. 


CUSTER COUNTY. 


Minn. 

Country rock and remarks. 

Ore and gangue. 

COLE DISTRICT. 

• 

• 

David City Lightning. 

Mica-schist, with much quartz on foot wall. Strike, X. and S.; 
dip, 85° W.; ore belt 8 feet wide. 

Quartz and schist, carrying free gold. 


Mica-echist; dip, N.; ore belt 30 feet wide. . 

Lenticular masses of smoky quartz, carrying free gold. 

CUSTER DISTRICT. 


Atlantic. 

Hanging wall mica-schist; foot wall quartzite. Strike, X. 5° W.; 
dip, 6U a W. 

Quartz, carrying free gold. 

Grand Junction. 

Mica-schist. Strike, X. 5° W.; dip, 45° W.; ore belt 70 feet wide. 

Auriferous quartz, with little silver, in a schist consisting of 
radiated aggregations of minute fibers of tremolite. 

Hartford. 

Mica-schist, sometimes garnetiferous. Strike. X. 5° W.; dip, 45° 
W.; ore belt 100 feet wide. 

Quartz and amphibolitic schists, carrying free gold. 

Mammoth. 

Mica-schist. Strike, X. 5° W.; dip, 45° W.: ore belt 100 feet wide. 

Quartz and schist, carrying free gold and some silver; garnet 
occurs with the quartz. 

Old Bill. 

Hanging wall quartzose mica-schist, with garnet and pyrite’i 
foot wall quartzite, with micaceous layers. 

Quartz and country, carrying gold and little silver. 

Old Charley. 

Probably Archaean schists; no specimens. Ore belt 300 feet wide. 

Quartz masses in fine-grained gneiss, carrying free gold. 


GEOLOGICAL SKETCH OF MONTANA. 

Physical description.— The territory of Montana, lying along the northern boundary of the United States, 
extends westward from the line of Dakota, at the junction of the Yellowstone and Missouri rivers, theoretically to 
the extreme crest of the Kooky mountains. 

The eastern half, which consists of the valleys of the Yellowstone and Missouri rivers and their immediate 
tributaries, belongs more properly to the plain country of the northern Missouri valley. This portion of the territory 
is largely occupied by various Indian reservations, and its mineral wealth has been but little explored. 

Of the mountainous western half, the northern portion, adjoining the British boundaries, is also but little known. 
From the southern boundary of Montana, near the heads of the Yellowstone and the Missouri rivers, the Rocky 
mountains assume a northwestern trend. The little chartographic knowledge obtained of this region is derived from 
the records of the Northwest Boundary survey and from the explorations for a route for the Pacific railroad made 
under the War Department, which give a partial knowledge of certain lines, between which are broad gaps whose 
topography is comparatively unknown. The Rocky mountains, which in Colorado are a compact series of chains 
having a general north and south trend, end abruptly in southern Wyoming; but in northwestern Wyoming they are 
represented by the Wind River, Shoshone, and Big Horn mountains, which take a general northwesterly direction. 
The Wahsatch system in Utah has also a north and south trend, and is separated from the Rocky Mountain system 
by the basin of the Colorado river. Through eastern Idaho this chain also loses somewhat of its continuity, and the 
Rocky Mountain system in Montana is apparently formed by the junction of these two systems of elevation. In 
geueral, the mountain regions in western Montana are less elevated than those of Colorado and Utah and abound 
in broad open valleys, so that in spite of the northern latitude the climate is relatively mild. They are well watered, 
the hills and valleys support an abundant growth of timber or grass, and in many of the valleys a limited amount 
of a griculture is possible. 

Geology".— Of the geology of Montana but little is definitely known, the work of the government geological 
surveys not yet having extended so far north. The surface of the eastern half of the territory is probably largely 
covered by the Tertiary and Cretaceous formations which are found on the great plains of the south, while along 
the large streams are broad alluvial valleys, which extend well up to the foot-hills of the mountains and are 
admirably adapted for agriculture. 

As well as can be determined from the scanty material at hand, the geology of the mountainous districts ot 
western Montana is more nearly allied to that of the Wahsatch range than to that of the Rocky mountains of Colorado, 
Indeed, the Arclnean uplift of the Front range of Colorado finds its northern continuation in the Black hills of 
Dakota on a line with the extreme eastern boundary of Montana. It has already been observed (a) that the 
Wahsatch range forms the geological center of the Cordilleran system, and that between the sedimentary series 
developed on either side of this central axis there is a great and characteristic difference. The Palaeozoic formations, 
which in Utah and Nevada reach an aggregate thickness of over 30,000 feet, in Colorado have an average of only 
about 5,000 feet. Over the Great Basin area the Triassic and Cretaceous rocks are entirely wanting, and those 
developed on the eastern slope of the Rocky mountains, extending in the Wyoming basin as far as the flanks of the 
Wahsatch, are entirely different from corresponding horizons in western Nevada and California. The heavy 
limestones of the lower portion of the Palaeozoic system are found to thicken as one follows the line of the Wahsatch 
northward through eastern Idaho. From the older sedimentary beds of Montana, as far as known, no fossils have 
yet been obtaiued by which to determine definitely the age of any particular horizon; but the character of 
specimens of limestone and argillaceous rocks received renders it probable that those developed in the mining regions 

a See Reports of the U. S. Geological Exploration of the Fortieth Parallel. 






































GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


95 


of Montana belong to the lower portion of the Palaeozoic horizon, the more so as they rest directly on granites or 
Archaean schists. The only geological data available are furnished by specimens collected in the southern central 
portion of the western half of the territory, viz, from Lewis and Clarke, Deer Lodge, Jefferson, Madison, and Beaver 
Head counties. Of the geology of the regions extending north from here to the British line, through Missoula and 
Choteau counties, but little information is available. That obtained from these counties, which is furnished 
simply by specimens of country rock brought in by the experts who examined this region, is too meager to afford any 
ideas of general structure ; but there would seem to be an upheaval of Archaean rocks, exposing gneissic formations, 
on a north and south line through the center of this region. Along this line is also a considerable development of 
so-called granite, in which the most valuable ore deposits occur. A very large portion of this granite, however, 
proves to be a diorite of somewhat singular character, possessing certain marked characteristics, which is found 
from Madison, through Deer Lodge, north to Lewis and Clarke county, and it seems probable that it is an eruptive 
body of Archaean age, distinct from the true Archaean granite. The specimens which have been microscopically 
examined were obtained from near the Lexington and Alice mines, at Butte City, and the Deer Lodge lode, in Deer 
Lodge county; also from Union lode No. 2 and Schafer Mill, in Lewis and Clarke county. It is a crystalline rock, 
containing both orthoclase and plagioclase feldspars, the latter being predominant, with but little quartz; also a 
large proportion of basic minerals, among which hornblende, augite, and biotite all occur. This association is the 
more remarkable, since it seems that these minerals are all original, and the hornblende is not, as would appear at 
first glance, simply a decomposition product of augite. Under the microscope the former is seen, indeed, to form in 
many cases the periphery of the augite masses; but it is not fibrous, like the uralitic products of hornblende 
decomposition, but clear and homogeneous. Hornblende also occurs in distinct individuals; and, moreover, there 
are distinct intergrowths of biotite and hornblende, both fresh and with the biotite leaves lying parallel to tbe 
orthopinacoid of the hornblende. It would seem, therefore, that at a certain period in the growth of the rock the 
formation of augite may have ceased and the hornblende have formed about the already existing augite particles. 
The augite is pale, and contains much magnetite in small grains. The biotite changes to a green mineral, which 
does not seem identical with the ordinary chlorite, and this, in turn, changes into epidote. Most of the biotite is 
tresh, and titanite, apatite, and magnetite are present. The type described is that from the Union lode. That from 
Schafer Mill contains more quartz than orthoclase, and some of the quartz is intergrown with orthoclase, so as to 
make a distinct graphic-granite structure, visible only under the microscope. Both augite and biotite are abundant, 
but hornblende is relatively rare. The country rock of the Lexington mine, at Butte, has the same general character 
as that of the type rock. Much of the hornblende is twinned, and intergrowth of biotite is common. The rock of 
the Alice mine, at Butte, is somewhat coarser grained than the others, and contains a less proportion of basic 
silicates, augite being entirely absent from the section examined. Mica and hornblende are about equal in quantity, 
and the hornblende has frequently the outlines of the prism, showing that it can hardly come from the decomposition 
of augite. The rock from Deer Lodge lode, McClellan’s Gulch district, Deer Lodge county, is somewhat different 
from all of the above. It contains much more quartz and orthoclase, and augite is wanting, although hornblende 
and biotite are similarly intergrown as in the type rock. It also contains apatite, a little magnetite, and a few pale 
crystals of zircon, but no titanite. A more detailed study of this interesting rock than it was possible to make by 
the aid of the few specimens collected by the census experts would be necessary in order to definitely determine 
its character. In the subjoined tables it has been provisionally called “diorite-granite”, to distinguish it from the 
normal type of granite which occurs in the same district, but whose structural relations to it are as yet unknown. 

Of rocks which could be definitely determined as belonging to the Secondary eruptive series but few specimens 
were brought in. There can, however, be no doubt that they are of frequent occurrence in the territory, and it seems 
probable that to this type may belong the so-called granites which overlie the contact deposits in limestone of the 
Bannack district. But little reliance can, unfortunately, be placed on the nomenclature given by miners to the 
rocks they find associated with their ores, since they, too, often pride themselves on having distinctive names of 
their own, quite independent of any scientific usage. The so-called porphyries reported from Montana mines 
have proved, where specimens have been sent in, to be more or less altered granites or gneisses. Of Tertiary eruptive 
rocks such great flows exist in Idaho on the south and west, and also in the Yellowstone park, that it is probable 
many may occur in the territory. The only definitely known occurrence is the rhyolite, which breaks through the 
diorite-granite at Butte City. 

Ore deposits. —The ores of Montana are mostly of gold, silver, and copper, either separately or in combination 
with two or more of these metals. Argentiferous lead ores also occur, but in far smaller proportion than in Colorado, 
and are seldom free from other base metals. These ores are found either in veins in the crystalline rocks or as irregular 
deposits in sedimentary rocks, sometimes crossing the strata, but generally more or less coincident with bedding- 
planes. Of the deposits in crystalline rocks the majority of the best known, and those whose bodies are strong and 
well defined, are of the class of metamorphic veins, i. e ., their vein material is a portion of the country rock, more or 
less altered along certain planes, in which silica, calcite, and metallic minerals have replaced portions or all of the 
original constituents. In these deposits there is, as a rule, no definite limit or wall, or, at the most, on one side 


96 


PRECIOUS METALS. 


only 5 and it is evident that there was no pre-existent open fissure, as is theoretically supposed to have been the 
antecedent condition of the “true fissure vein”. It may also be said that, as far as our present knowledge goes, 
there is no valid reason for supposing that such deposits are any less permanent or rich than those which may show 
evidence of having been deposited in a pre-existing open fissure. 

In some cases gold-bearing ores seem to be simply impregnations of the gueissic country rock with auriferous 
pyrites, and probably occur in lenticular interlamina ted quartz masses, such as on a very much larger scale 
constitute the so-called gold veins of the Black hills of Dakota. Deposits in limestone seem to be here, as 
elsewhere, very irregular in form, but tend to follow bedding or contact planes and cross-joints which have yielded 
more easy access to metallic solutions. Owing to the superior thickness of the Paheozoic formations in this region 
the vertical range of the deposits is probably much greater than in Colorado. 

A considerable proportion of the ores are auriferous pyrites and quartz, sufficiently oxidized to mill freely; but 
the greater value and bulk are those of more complex composition, which require to be smelted. These have 
two characteristics which distinguish them from the ores of Colorado : first, a usual presence of copper, rather than 
of lead, as a silver-carrier, and of manganese, instead of iron, in that part of the ore which goes into the slags in 
smelting. Chalcocite, or copper glance, is one of the most common minerals, and oxide of manganese, passing 
into carbonate below the water level, is exceptionally frequent. No data are at hand for making even an 
approximately complete list of the minerals which occur in the territory. 

Placer deposits. —Until within a comparatively few jears the main precious-metal production of Montana 
has been derived from its placer deposits, which are exceptionally rich. Estimates place their total yield at over 
$50,000,000, but it is impossible to say how close an approximation to the truth these estimates may be, since the 
grounds on which they are based are not given, and the determination of the yield of placer mines is the most difficult 
task the mineral statistician has to undertake. The first deposits were discovered in 1801 in the Pioneer district, 
on Gold creek, a branch of Deer Lodge river, in the county of the same name. For many years the production of 
the placer mines was very large; and a great many are worked at the present day, although their production has 
somewhat fallen off by the working out of the exceptionally rich deposits. Hydraulic mining is carried on to a 
very considerable extent, and many Chinese miners find ample remuneration in working over abandoned gulch mines. 
Owing to an unfortunate combination of circumstances the census data were collected very late in the season, when 
the placer mines were mostly abandoned for the winter; and the data iu regard to these deposits are, consequently, 
very incomplete. The deposits which are worked seem to have been found mostly iu rather open valleys, but 
comparatively high up in the mountains, and consist consequently of rather coarse gravel. For deposits of this 
character they are exceptionally thick, varying according to data from 5 to 65 feet; and in many cases actual bed-rock 
had not been reached, but only a clayey seam or false bed-rock, below which the gravel is said to be barren. 

From many of the deposits fossil shells and petrified bones and tusks are said to have been obtained. No 
specimens, however, have been sent in. It seems likely, therefore, that these deposits are, as a rule, older than 
the ordinary river gravels, and may date back to-the flood period following the Glacial epoch. Placer deposits are 
known to be worked in Beaver Head, Madison, Gallatin, Meagher, Jefferson, Deer Lodge, Lewis and Clarke, and 
Missoula counties, the most productive of which have been those of Alder gulch, a branch of the Stinking Water, 
at the head of the Jefferson river, in Madison county. Next to these are those of Deer Lodge county, the most 
important of which is the Pioneer district, and several in the neighborhood of Butte City which are tributary to 
the Deer Lodge river, the Henderson district, near Flint creek, and the McClellan Gulch district, at the head of the 
Big Blackfoot river. 

in Lewis and Clarke county the Last Chance district, near Helena, has been a large producer ; and important 
deposits have been worked on both sides of the Missouri river, both in this and in Meagher county, as also on the 
east slope of the Big Belt mountains of the latter county. Tlacers have also been worked in Gallatin county north 
of the National park, along the tributaries of the Yellowstone river. Iu Beaver Head county the placers near 
Banuack hate a bed-rock of conglomerate with lime cement, containing shells and large bones, which must, it seems, 
have as early an origin as the Glacial epoch. The gold is coarse shot gold, with a relatively large proportion of 
nuggets as large as walnuts; and that derived from the Montana placers, in general, has a higher average 
srradc of fineness than that of other territories. 


DEER LODGE COUNTY (SILVER BOW COUNTY). 

The most important mining district in the state is Summit valley, near Butte City, which, since the legislative 
action of February, 1881, is now included in the new county of Silver Bow. The ore deposits of this district all 
occur either in true granite or in the diorite-granite already described. The majority of the veins from which data 
are available have an east and west strike and dip at a high angle to the south. Besides the granite country 
rock, rhyolite occurs, which forms the so-called butte from which the town derives its name, ramifications from 
which body, it is suspected, may be found in the neighborhood of some of the important mines. The veins belong 
certainly to the type of metamorphic veins, i. e., although the richer part of the ore is often found in a gaugue of 
almost exclusively siliceous material and with a fairly defined wall on one side, on the other there is no definite 


GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


97 


limit, but the country rock is found to yield pay material for a varying distance from the main ore body, and the 
limit to which the impregnation has extended is, consequently, not determined, since only that which it would pay 
to work is extracted. The most important mines of the district are the Alice, Lexington, Belle, Gagnon, and North 
Star. Ores rich in copper and silver, antj carrying an exceptionally large proportion of manganese minerals, are 
the prevailing type. 

The Flint Creek district, near Phillipsburg, to the northeast of Butte City, has silver-bearing ores carrying 
zinc, copper, and lead minerals in a limestone generally white and crystalline. In the case of the Salmon mine 
grauite is reported as occurring on the hanging wall of the vein, but as no specimens were returned it seems 
questionable whether it may not be a crystalline porphyry. 

In the McClellan Gulch district, at the head of the Big Blackfoot river, auriferous quartz is found in a rock 
resembling the diorite-granite of Butte City. 

LEWIS AND CLARKE COUNTY. 

The principal mines of Lewis and Clarke county appear to be near Helena at its southern extremity and along 
the heads of Silver creek a short distance north. At Helena they are mainly gold-bearing veins in granite. In 
the Silver Creek region they are also gold-bearing ores, containing a little silver, but occur in slates and slaty 
limestones; and although standing at a high angle, and called fissure veins, it would seem that in some cases at 
least they are more probably segregations of quartz and mineral in bodies lying parallel with the formation. 

JEFFERSON COUNTY. 

In Jefferson county the ores carry both gold and silver in varying proportions, and the mines occur in various 
districts on either slope of the mountains lying west of the Missouri river. The ores are comparatively free from 
base metals, and occur in felsite-porphyry and other undetermined eruptive rocks, and in limestones parallel with 
the stratification-planes. 

MADISON COUNTY. 

In the northeast portion of Madison county, near the Jefferson river, are the Silver Star districts, whose ores 
occur mainly in gneiss, and are gold-bearing, with a slight admixture in some cases of lead and copper ores. The 
Broadway mine is reported to be a bedded deposit at the contact of limestone with granite. 

In the Mineral Hill district, at the head of Willow creek, north of Virginia City, galena and quartz, carrying 
both gold and silver, are found in gneiss; and in the Bed Bluff and Hot Springs region, near the Madison river, are 
ores of galena and pyrite, also mainly in gneiss, carrying both gold and silver. 

BEAVER HEAD COUNTY. 

In Beaver Head county, near Baunack City, auriferous pyrite in quartz, sometimes associated with galena, is 
found in limestone, with a hanging wall of so-called granite. The strike of this formation seems to be uniformly to 
the northeast, with a shallow dip of from 15° to 20° to the south and southeast. As already stated, it seems probable 
that, the so-called granite is a quartz-porphyry or diorite. Slates and limestones can be traced northward from 
Bannack, through Argenta, to Glendale, near Big Hole river. At first they preserve the westerly dip observed 
near Bannack, which gradually steepens, and becomes vertical some 15 miles north of Argenta. The formation 
from here to Glendale dips to the eastward. Along Trapper creek, which flows into the Big Hole from the west, 
are easterly-dipping slates, apparently underlying the limestone which is found at Glendale. At its head is a 
cliff about 1,000 feet in height of blue-gray limestone beds, underlaid by black bituminous shale, dipping 16° to 
the westward; half-way up the cliff are the deposits of the Hecla Consolidated mines, which are masses of 
argentiferous galena, zincblende, copper, and iron pyrite, and their oxidation products, occurring on the stratification - 
planes of the limestone at different horizons. These ores are smelted to a lead bullion and a copper matte carrying- 
silver. Big Hole river, some 8 or 10 miles higher up, runs through a canon cut in gneiss, and at Dewey’s flat, above 
the canon, abundant gold-bearing quartz veins in gneiss are said to occur. 


vol 13-7 



98 


PRECIOUS METALS. 


DEER LODGE COUNTY, (a) 


Mine. 

SUMMIT VALLET DISTRICT. 

Alice. 

Anaconda. 

Anglo-Saxon. 

Anselmo. 

Belle. 

Clear Grit. 

Colusa. 

Cora. 

Gagnon. 

High Ore. 


Country rock and vein. 


Diorite-grnnite, rich in plagioclase, with some augite. Vein: 
strike, NE.; dip, 65° KW.; 35 feet wide. 

Granite (?). Vein: strike, E. and TV.; dip, 75° ; 8 feet wide. 

Granite. Vein: dip, 47° S.; 2£ to 5 feet wide. 


Granite, containing pyrites. Vein: strike, E. and TV.; dip, 7° S.; 
2 to 5 feet wide. 

Diorite-granite. Vein vertical; strike, E. and W. 


True granite. Vein : strike, NW.; dip, 70° STV.; width, 15 to 17 
feet (2 feet productive). 

Granite (?). Ho specimens. Vein: strike, NW.; dip, 70°; 14 feet 
wide. 

Granite (?). Ho specimens. Vein vertical; strike, E. and TV.; 
26 feet wide, including horse of porphj ry. 

Granite. Ho specimens. Ho distinct walls. Vein: strike, E.; dip, 
80° S.; width, 150 feet (8 feet pay). 

Decomposed granite. Vein : strike, E. and TV.; dip, 45° S.; 12 to 
16 feet wide. 


Ore and gangue. 


Hative silver, and sulphide, with carbonate of manganese, 
quartz, and pyrite, cairying gold and silver. Gangue: altered 
country. 

Chloride of silver, malachite, azurite, chalcocite. Gangue: sili¬ 
ceous, may be altered porphyry. 

Cerussite, caibonate of manganese, and sulphide of silver in 
quartz; yellow stains of antimony; carries silver and little 
gold. Gangue: decomposed granite. 

Hative silver; argentite, galena, pyrite; traces of manganese, 
copper, and gold in quartz. Gangue: decomposed granite. 

Massive chalcopyiite, with pyrite, lrornite, freibergite (?), and 
native silver, with but little quartz. Gangue: clay, withrounded 
granite pebbles. 

Cellular quartz, containing sulphuret of silver; little gold. 

Chalcocite, massive and impregnating the granite. Gangue and 
horse material; decomposed quaitz-bearing granular lock. 

Ho specimens. “Copper, lead, a little zinc and silver, and an¬ 
timony." 

Chalcocite, silver-hearing. Gangue: mainly quartz, with pyrite. 

Chloride of silver (?) in cellular quartz ; little gold. 


Late Acquisition 

Lexington. 

Morning Star.... 

Mountain. 

Kational. 


Diorite-granite. Vein : strike, E. and "V. ; dip, 75° S.; 5 feet i 
wide. 

Diorite-granite. Vein: strike, E. and TV.; dip, 30° S.; 8 feet 
wide. 

Granite. Vein vertical; strike, E. and TV. j 

Granite. Ho specimen. Vein: strike, NW. and SE.; dip, 75° S.; 

8 feet thick. 

Decomposed granite. Vein: strike, E. and W.; dip, 80° S.; 20 feet 
wide. 


Hettie. 

North Star 


Shakspeare. 

Shonbar . 

Silver Bow Mining Company 
(13 mines reported in one 
schedule). 

Springfield. 


Star TVest 
Stevens... 


Granite. Vein: strike, E. and TV.; dip, 70° S.; 5J feet wide_ 

Ho specimens. Called granite-porphyry, may be rhyolite. Vein: 
strike, E. and TV.; dip, vertical; 50 toot wide. 

Granite (diorite?). Vein: dip, 90°; 20 to 40 wide; foot wall not 
found. 

“Soft granite." Ho specimens. Vein: strike, E. and TV.; dip, 
70° S.; 12 feet wide. 

Granite and syenite (?). Ho specimens. Veins: strike, about E. 
and TV. ; dip, lrom 45° to 90°. 

“Hard granite.” Ho specimens. Vein : dip, 70° S.; pay-streak, 
4 feet wide on foot wall. 

Hanging wall like granite. Foot wall diorite (?). Vein: strike, ? 
dip, 36° S. 

Altered syenite (diorite?). Vein: strike, E. and TV.; dip, 60° S.; 
4 feet wide. 


Volunteer 


\V abash 


“ Soft granite.” Veins (2) 16 feet apart; strike, E. and TV.; dip, 
45° S.; one 3 feet, the other 8 to 15 feet wide, the former the 
richer. 

Granite. Ho specimens. Vein: strike, E. and TV.; dip, “10°” j 
(probably 80°) H.; 100 feet wide; pay-streak 2 to 6 feet. 


INDEPENDENCE DISTRICT. 


Pyrite and chalcocite in quartz; galena and chlorides said to 
occur; little gold. Gangue: decomposed country rock. 

Galena and cerussite, with rhodonite; silver and gold bearing. 

Auriferous pyrite; native silver and sulphuret in quartz. Gangue: 
altered granite. 

Copper. Ho specimens. 

Chalcocite and pyrite, carrying silver. 

Psilomelane and horn-silver. 

Chloride, black sulphuret, afad native silver. Ho specimens. 

Largely chalcocite, carrying little silver. 

“ Black manganese,” carrying silver and little gold. Ho speci¬ 
mens. 

Ores carrying galena, cerussite, pyrite, chalcopyrite, and sul- 
phurets. Ho specimens. Veins said to be inclosed in porphy¬ 
ry. probably decomposed granite (diorite). 

“ Sulphurets of silver and iron.” Ho specimens. 

Freibergite and pyrite, with manganese mineral. 

Cellular quartz stained yellow, carrying gold and silver. No 
mineral visible. 

Massive zincblende and freibergite, said to contain also horn- 
silver and galena. 

Cellular quartz with yellowish green coating, said to contain 
gold and chloride of silver. Gangue: a crumbling mass of quartz 
and feldspar stained reddish yellow, probably altered country. 


Mountain Boy 


Self-rising 


FLINT. CREEK DISTRICT. 


Granite. Vein: strike, about E. and TV. ; dip, 70° S.; 2 feet wide 

“Porphyry" (?). No specimens. Vein: strike, E. and TV.; dip, 
vertical; 3 to 7 feet wide. 


Quartz, impregnated with galena; pyrite, rhodoehrosite, with 
native silver on joint-planes. Gangue: decomposed country 
rock. 

■ Black oxide of manganese, with gold, silver, and copper. Ho 
specimens. 


Algonquin. 

Salmon. 

Speckled Trout. 

Hope —..•. 

Scratch Awl. 


"White granular limestone (dolomitic?) near granite. Deposit : Galena, blende, gray copper, etc., in quartz. Oxide of manga- 
strike, N. 20° E. ; dip, 45° E., in irregular bodies. nese and pyrite also occur; silver bearing. 

Granite (?) hanging wall. Ho specimen. Limestone foot wall. I Quartz, with zincblende and copper stains, carrying silver. 
Deposit: strike, N. 20 E. ; dip, 45° E. 

Gray crystallinelimestone, fine-grained on hanging wall, coarser- Mainly crystalline zincblende and argentiferous galena; said to 
grained on foot wall. Vein: strike. NE.; dip, 80° SE.; 2 feet ; carry nr by silver, 

wide. 

Fine-grained yellowish limestone; ore deposit in bedded masses; Quartz, impregnated with black sulphurets of silver and car- 
strike, E. and TV. ; dip, 32° ; 4 to 9 feet thick. bonate of copper. 

Limestone, white and crystalline, on the north wall; thinly Stained quartz, with oxides of manganese and copper, carrying 
bedded and slaty on the south wall. Vein : strike, E. 6° S.; dip, silver, 
vertical; 2 feet wide. 


m’clellan’s gulch district. 


Deer Lodge 


Diorite-granite. Vein: strike, N. 20 E.; dip, 20° TV.; 1 to 2 Iron-stained quartz, 
feet wide, 


McClellan’s Gulch lode 


Diorite-granite. Vein: strike, HE.; dip, 20° S. E 


Iron-stained qnartz. 


a In February, 1881 , a portion of Deer Lodge county, including the Summit Valley district, was set off into a separate county, called Silver Bow. 






























































GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


♦ 


99 


LEWIS AND CLARKE COUNTY. 


Mine. 


SILVER CHEEK DISTRICT. 


Countrv rock anil vein. 



Ore and gangue. 


Albion. Dark slate. Vein: strike, E. 8J° N.; dip, 70° N.; 18 inches to 

I 11 feet thick. 

Penobscot, Snowdrift, and Tough greenish slate, with imperfect bedding; small quartz 
Courage. 1 veins. Vein: stiike, E. and \V. ; dip, 7U° N.; 4 to 18 feet wide. 

Belmont.i Slate at surface. No specimens. Normal granite in depth. 

Vein : strike, E. and W.; dip, S.; average width, G feet, with 
two branches. 


Quartz, with oxides of iron and manganese, little lead and cop¬ 
per, carrying gold and little silver. 

i Quartz, with oxides of iron and manganese ; stibnite in pockets; 
carries gold and trace of silver. 

I Quartz, with some calcite, carrying gold and silver. 


STEMPLE DISTKICT. 

Hickey and Bluebird. 

Mount Pleasant. 

Sandford . 

Whip-poor-will. 

OTTAWA DISTRICT. 


Dark compact slate, with imperfect bedding ; ore bodies ; strike, Mixture of quartz and feldspar, carrying gold ; gangue of fine, 
E. and W.; dip, 80° S. compact limestone in center of ore body in depth. 

Slaty limestone. Deposit: strike, E. and W.; dip, 80° S.; width, Ore deposit like the former. 

5 feet. 

Same character as Hickey and Bluebird, of which it is a con¬ 
tinuation. 

Slaty limestone. Vein: strike, E. and W.; dip, 75° N.; 3 feet I Iron-stained quartz, 
wide. 


Drumlommond. 

OWYHEE DISTRICT. 


Syenitic granite, with a little quartz. Vein: strike, E. and W.; 
dip, 70° S.; GO feet wide (40 feet long). 


Mixture of quartz and feldspar, stained with azurite and iron oxide. 


Union lode No. 2 


Diorite-granite.withbiotite, hornblende, andaugite. Vein: strike?; 
dip, 30° N.; 3 feet wide. 


White gold-bearing quartz. 


JEFFERSON COUNTY. 


CATARACT DISTRICT. 



Boulder . 

Decomposed porphyry. Vein: strike, N. 70 W.; dip, 85° NE.; 
7£ feet wide. 

Iron-stained quartz, carrying gold. 

Mantle. 

Syenite (?) containing a little quartz. Vein: strike, ENE.; dip, 
vertical; 4 feet wide. 

Gold-bearing quartz, with pyrite; little silver. 

CEDAR PLAINS DISTRICT. 



Keating. 

White homogeneous felsite, impregnated with pyrites. Vein: 
strike, N. and S.; dip, 85° W.; 3 feet wide. 

Massive pyrite, carrying gold and silver. 

ELKHORN DISTRICT. 



Alta. 

Compact felsitic porphyry. Vein: strike, NE.; dip, 60° NW.; 8 
to 10 feet wide. 

Quartz, carrying galena and pyrite, silver, and a little gold. 

A. M. Holter. 

Limestone, thin bedded and compact on hanging wall; granular, 
resembling a sandstone on foot wall; ore body, dip 45° to the 
north with the stratification. 

Quartz, with argentiferous galena, some native and horn-silver. 

MOUNTAIN DISTRICT. 



Little Giant. 

Greenish eruptive rock; undeterminable. Vein: strike, E. and 
W.; dip, 80° S.; 4 to 6 feet wide. 

Iron-stained mass, quartz and clay carrying gold. 

DISTRICT NOT ORGANIZED. 


, 

Bonanza Chief. 

SILVER STAR DISTRICT. 

No specimen. “ Quartzose rock,” “bedded mass in granite.” 
Dip, 20° NE. 

Iron-stained siliceous matter, containing gold and traces of silver. 

Aurora Borealis. 

Fine-grained gneiss. Vein: strike, E. and W.; dip, 45° S.; 2feet 
wide. 

Gold-bearing quartz with galena; little carbonate of copper and 
iron oxide. 

Broadway. 

Hanging wall dark impure limestone; foot wall granite. De- 

Yellow ferruginous jasper, with spots of hematite, chalcedony, 

posit: strike, NW. and SE.; dip, 38° S.; thickness, 15feet. 

and calcite in the fissures; carries gold. 

Grasshopper and Cricket. 

Syenite(?), probably gneiss. No specimen. Vein : strike, E. and 
W.; (lip, 50° S.; 5 to 6 inches wide. 

Iron-stained gold-bearing quartz. 

Grubstake.,. 

0 

Even-grained gneiss. Vein: strike, NW.; dip, 45° NE.; 2 feet 
wide. 

Decomposed yellow rock, probably gneiss carrying silver. 


MADISON COUNTY. 


• • 


HOT SPRINGS AND RED BLUFF 
DISTRICTS. 

Boaz. 

♦ 

Gneiss. Vein : strike, NW.; dip, 45° E.; 2 feet wide. 

Crumbling, stratified rock, iron-stained, and carrying gold. A1 
tered country. 

Cordwainer. 

Fine-grained biotite-gneiss. Vein: strike, NW.; dip, 50° NE.; 
2£ feet wide. 

Crumbling, iron-stained gneiss, carrying gold ; little copper. 

Red Bluff. 

Gneiss. Vein : strike, E. and W.; dip, 41° N.; 3 to G feet wide— 

At surface red or blue jasper, with some pyrite and galena 
carrying gold and silver. Below water level solid mass o 
pyrite and galena, with little quartz. 

Red Chief. 

/ 

Granite!?). No specimens. Vein : dip, 48° NE.; 4 feet wide- 

Iron-stained quartz, carrying gold and silver. 

MINERAL HILL DISTRICT. 



White Pine. 

Gneiss, with rhombic pyroxene. Vein: strike, E. and W.; dip, 
45° S.; 18 inches wide." 

Massive quartz, with some galena, carrying gold and silver. 


































































J 00 


PRECIOUS METALS. 


i 


BEAVER HEAD COUNTY. 


Mine. 

Country rock and vein. 

Ore and gangue. 

BAXNACK DISTRICT. 



Dakota and Blue Grass. 

Hanging 'wall granite; foot wall limestone. No specimens. De¬ 
posit: strike, NE.: dip, 15° SE.; 8 feet thick. 

Quartz, pyrite, and siliceous oxide of iron, carrying gold. 


Excelsior. 

Hanging wall granite (?) and trap; foot wall limestone. No 
specimens. Deposit: strike, NW.; dip, 20° SE. ; 8feet thick. 

Iron-stained quartz and pyrite. 


French . 

Hanging wall granite (?); foot wall limestone. No specimens. 
Deposit: strike, E. and W.; dip, 15° S.; 15 to 40 feet thick. 

Siliceous iron, with pyrite, carrying gold. 


Golden Leaf. 

Same ns French. Deposit: 10 to 80 feet; dip, 15° S.; strike, NE. 
and SW.; 10 to 50 feet thick. 

Oxide of iron, free gold, argentiferous galena. 


Springfield . 

Hanging wall granite (?); foot wall limestone. No specimens. 
Strike, NE.; dip, 15° S.; 5 feet thick. 

Auriferous iron-stained quartz. 

"Washington. 

Like the preceding. 


BALD MOUNTAIN DISTRICT. 



Elkliom. 

J 

Granite. No specimens. Vein : strike, NE. and SW.; dip, 88° N. 

“Zincblende, black copper, gray copper, chloride, and native 
silver.” No specimens. 

TRAPPER DISTRICT. 



Hecla.... 

Dolomite, blue and gray. Ore deposit follows the stratification- 
planes. Strike, N.; dip, 10° W.; 2£ feet thick. Several bodies. 

Contains galena, cernssite, calamine, and copper minerals. Gangue: 
white crystalline limestone. 


Keokuk . . 

Limestone, siliceous on hanging wall, crystalline on foot wall. 
Ore deposit following the stratification-planes. Dip, 35° SW. 

Oxides, carbonates, and sulphurets of silver, lead, and copper. 
No specimens. 


GEOLOGICAL SKETCH OF NEW MEXICO. 

The territory of New Mexico, adjoining Colorado on the south, has a somewhat larger area, and is included 
between the one hundred and third degree of longitude west of Greenwich and the thirty-second west of Washington, 
and extends from the thirty-seventh degree of north latitude to the boundary of Mexico, which, except in the 
southwestern corner, is formed by the thirty-second degree of north latitude. Its climate is even drier than that 
of Colorado, which may be due to the fact that it has no concentrated high mountain mass to act as a condeuser to 
the moisture-laden winds coming from the southwest. The mountain systems of Colorado end abruptly near its 
northern border, the Colorado range continuing with a gradually decreasing elevation as far south as Santa Fe, 
while the San Juan mountains, to the west of San Luis park, sink beneath the Cretaceous plains almost before the 
boundary is reached. Its surface is made up of an irregular series of detached mountain chains, stretching across 
the middle of the territory in a southwesterly direction, with a mesa country, belonging to the Colorado plateau 
region on the northwest, and broad arid plains, a continuation of those in northern Texas, stretching to the east ward. 
Across the middle of this area from north to south runs the Rio Grande river, whose valley presents many analogies 
with that of the famous Nile valley of Egypt. Its climate is warm and equable, and its alluvial soil, which occupies 
a comparatively narrow strip on either side of the river, in general not more than 2 miles in width, is of exceptional 
fertility. Like the Nile, it is subject to periodical overflows, and the area of its arable land can probably be 
increased by a more perfect system of irrigation than lias been carried on by the Mexican population which at 
present occupies it. With the exception of this valley, there is little, if any, land in the territory which can be 
considered available for agriculture, not from any want of fertility of soil, but from the absence of water for 
irrigating purposes. The main wealth of the territory lies, therefore, in its grazing lands audits mineral resources. 

Our geographical knowledge of this area is as yet extremely imperfect, being derived only from the meander 
lines made in early years by various government expeditions in exploring routes for a Pacific railroad and from 
detached maps of portions of the central and northern regions made by the explorations west of the 100th meridian 
under Lieutenant Wheeler. 

In regard to its geology our information is equally fragmentary, being derived from the notes made by 
Professors Jules Marcou and ,1. S. Newberry, who accompanied the earlier railroad explorations, and nf Messrs. G. 
K. Gilbert, E. E. Howell, and Professor J. J. Stevenson, who accompanied different parties of the Wheeler 
exploration. The census material with regard to this territory is also exceptionally incomplete, owing to the fact 
that Colonel Charles Potter, to whom was intrusted the duty of visiting and reporting on its various mining 
districts, was treacherously waylaid and killed by a party of seven Mexican robbers while in the discharge of this 
duty, and while his work, though nearly completed in the field, still needed liis personal supervision to put it into 
an intelligible form. 

General geology. —The Archaean island which stretched through the state of Colorado from its northern to 
its southern boundary ended abruptly in New Mexico, its continuation to the southward being marked only by a 
series of more or less submerged reefs in the ocean, which covered this area until the close of the Cretaceous period. 
Up to this time, therefore, the waters of the ocean had free access to the Colorado plateau region, and at the present 
day the coal-bearing or Cretaceous rocks are known to extend over a great portion of the territory. Owing to 
the limited rainfall, the valleys and mountain slopes are much more heavily covered by Quaternary debris than those 

































GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 


101 


ot Colorado, and the character of the underlying rocks is therefore more difficult to recognize. The Cretaceous 
formations are, however, known to extend from the plain country westward to the Rio Grande valley, and in the 
northwestern portion of the territory to connect with the Colorado plateau region, while they still form the surface 
rock over a very considerable area. In the latter region they are known to extend beyond its western boundaries, 
but in the mountain region, in the southwestern portiou of the territory, they have either been entirely eroded off, or 
else, owing to some dynamic movement later than the Palaeozoic period, as yet unproved, they were not deposited* 
Of eruptive rocks there is considerable development of quartz-porphyries and other Secondary rocks, especially in 
the southwestern portion of the territory; but no sufficient study has been made of them to determine definitely 
their age or relation to the Palaeozoic beds in connection with which they are found. The only known Tertiary beds 
are those near San lldefonso, which are supposed to be of Pliocene age. As yet, therefore, there is no record 
to determine the period at which the Tertiary eruptive rocks, which are so largely developed in the territory, 
were first poured out on the surface. Of these, as Mr. Gilbert shows, an immense crescent-shaped area extends 
through eastern Arizona and western New Mexico to the volcanic group of the San Francisco mountain at its 
northwestern point, and to that of Mount Taylor, in New Mexico, at its northeastern. They also cover considerable 
isolated areas to the east of the Rio Grande. That eruptive activity has continued until comparatively recent 
times is proved by the existence of numerous actual craters and cinder-cones in a region 35 to 40 miles southwest 
of Mount Taylor, from which streams of lava flowed out in every direction, extending at least 50 miles to the 
westward and to an unknown distance to the eastward. These recent,lava flows are, according to Mr. Gilbert, 
all basaltic, while the mass of Mount Taylor consists of an older eruptive rock, described by him as something 
between a basalt and trachyte, and which, from aualogy with other regions, may be supposed to be either andesite or 
a still earlier porphyrite. Professor Stevenson also describes extinct craters as existing to the east of Santa Fe near 
the Turkey mountains and flows of basaltic lavas filling the canon of the Mora river. The northwestern part of 
the territory, therefore, which, from the Nacimiento range westward, belougs to the mesa region, and south of the 
Carboniferous anticlinal of the Zufii range consists a broad belt of lava extending to the plains of San Augustin, is 
covered by rocks of too recent age to afford much promise to the prospector. It is in the mountain groups 
stretching across the territory to the southeast of this region that the principal developments have thus far been 
made. Among these Mr. Gilbert distinguishes two prevailing trends—a northwesterly and a nortli-and-south 
direction. The former, which is more common in the southwestern portion of the territory, he considers as belonging 
to a portiou of the Basin range system, which stretches through Arizona in the direction of the Sierra Nevada; 
the latter he connects with the Colorado system. In these different regions the rocks thus far recognized are 
either Archaean or Palaeozoic. Granite and gneiss are often found as a nucleus, and here, as elsewhere, are distinctly 
unconformable with the later beds of the Palaeozoic formations, which consist of quartzites, sandstones, limestones, 
and shales. Fossil evidence has been found of the existence of the Cincinnati group of the Silurian, the Waverly 
or sub-Carboniferous, and the characteristic Carboniferous limestones of the Rocky Mountain region. Of Mesozoic 
formations the Trias is recognized in the northern portion, and is described by Professor Stevenson as being extremely 
thin or at times entirely wanting along the edge of the mountains northeast of Santa FA The aggregate thickness 
of the Cretaceous rocks, which consist, as elsewhere, of sandstones and shales, is given by Professor Stevenson at 
2,000 feet. Mr. Gilbert states that coal is found throughout this entire formation, but only that of the middle 
is of economic importance. Professor Stevenson, on the other hand, makes the Galisteo beds, which have been 
practically developed in the northeastern part of the territory, belong to the Laramie group, or extreme upper member 
of the Cretaceous. Of the age of the coal-beds which have recently been developed in the neighborhood of the Rio 
Grande valley in the central and southern portion of the territory no information is available. In the succeeding 
description will be given the few facts it has been possible to obtain with regard to the geology of the mining 
regions thus far developed, following as far as possible the division by counties. 


COLFAX COUNTY. 


The western portion of Colfax county includes the southern end of the Rocky mountains, locally called the 
Taos and Bahly ranges, which consist of a nucleus of Archman, overlaid by Carboniferous limestone and flanked 
by Mesozoic beds. Throughout the region there is a considerable development of eruptive rocks classed as trachytic, 
and on the adjoining plains, on either side, are recent flows of basalt. Partially included in the range is the 
longitudinal Moreno valley, whose Quaternary deposits are said to constitute rich gold placers. Besides the placers, 
gold veins are said to have been developed, but no working mines are reported. Specimens of gray copper ore, 
associated with coal, have been brought in from points along the eastern foot-hills of the mountains. Their geological 
position is not known The matrix is a sandstone resembling those of the Cretaceous formation, and it may be 
that they occur in connection with the singular longitudinal dike mapped by Professor Stevenson. Galena and 
considerable placer deposits occur in Taos county, adjoining Colfax on the west. 


102 


PRECIOUS METALS. 


SANTA F.fi COUNTY. 


Tlie oldest mines of tlie territory, said to have been worked by the Spaniards when they first came here, over 
three centuries ago, are probably in Santa F6 county. 

The Los Cerillos district embraces the Los Cerillos mountains north of the Galisteo river, and the Ortiz mountains 
to the south. In the former an eruptive rock, probably rhyolite or trachyte, breaks through the Cretaceous strata. 
In this are found irregular, thin deposits of galena and the celebrated turquoise mines, which have been worked 
for years both by Mexicans and Indians. This mineral occurs apparently as au impregnation along the cleavage 
fiices of the country rock. Along the Ortiz mountains and the Placer mountains to the south are valuable placer 
deposits, which in places have been penetrated GO feet without reaching bed-rock. But little is known of their extent 
or character, and, owing to the want of water, they have thus far been but little developed. The Placer mountains 
consist of Archaean rocks overlaid by Carboniferous limestone. Veins of auriferous pyrites are said to occur in the 
Archaean; also magnetic iron ore. In the limestones are deposits following the stratification and occurring in 
connection with what is called porphyry, which contain both auriferous pyrites and sulphurets of copper, more 
or less oxidized, carrying silver. 


In Bernalillo county the Sandia mountains, which rise abruptly to the east of Bio Grande valley, are formed, 
according to Marcou, of Carboniferous strata dipping to the eastward, and have been apparently lifted to their 
present position by a fault. On their slopes occur also rich placer deposits. West of the Rio Grande copper has 
been obtained from the sandstones of the Trias in the neighborhood of Abiquin. The ores are found as carbonates 
and oxides, replacing fossil plants. 


SOCOEEO COUNTY. 

In the Socorro mountains, lying opposite the town of Socorro, on the Rio Grande river, according to 
Professor B. Silliman, (a) are several large veins of heavy spar running in a northeast and southwest direction and 
dipping 40° to the northwest, carrying chloride of silver and vanadium-bearing mimetite. The Magdalena 
mountains, 30 miles west of this, consist, according to the same authority, of slates, limestones, and quartzites, resting 
on gneiss and traversed by porphyritic eruptions. The Juniata lode is described as a vertical deposit of lead 
carbonates between^orphyry and slates reaching a maximum thickness of G5 feet, but of low grade in silver. Galena 
and zincbleude, with calamine and anglesite, are also found in the same deposit. 

In the Oscuro mountains, to the east of the Rio Grande, are deposits of copper glance, azurite, and malachite, 
carrying a little silver and gold in a siliceous conglomerate. These ores, like those already mentioned, are associated 
with remains of fossil wood and various plants, and are said to carry from 10 to GO per cent, of copper. This 
conglomerate, because of the resemblance of the deposits to those of Russia, which occur at this horizon, is regarded 
as of Permian age by Professor Silliman. The reason for such determination seems rather inadequate, in view of the 
fact that the Permian group has not yet been definitely recognized in the Rocky mountain system, to which these 
deposits belong, and that the beds in which similar deposits have been found in Colorado and New Mexico have 
hitherto been determined as Triassic. 

The Negretta or Black range extends across Socorro county into Grant county, adjoining, and is apparently 
connected with the Miembres range. It is so called because of the dark-colored firs which cover it. According 
to Professor Silliman, this range is intersected by powerful lodes carrying gold, silver, copper, zinc, aud lead, but no 
indication is given with regard to the character of the country rock, except that porphyry is mentioned as inclosing 
one vein. In the western portion of the county, at the head of the San Francisco river, is the Mogollon district, in 
which islands of Archaean granite, with Palaeozoic rocks resting on them, occur on the southern border of the lava 
area already mentioned; and in the limestones of the latter are rich deposits of copper, in some cases carrying 
both gold and silver. No returns from individual mines are at hand. 


LINCOLN COUNTY. 

In Lincoln county, to the east of Socorro county, about 125 miles from the Rio Grande valley, is the White 
Oaks district, in a mountain group generally known as the Sierra Blanca. Gold ores are reported as discovered in 
this district, but no reliable data are at hand as regards either their value or the geology of the district. 


DONA ANA COUNTY. 

In the Organ mountains, to the east of the Rio Grande, 15 miles from Las Cruces, argentiferous galena ores are 
reported. Near Hillsboro’, on the west of the Rio Grande, are placer deposits, and gold veins are said to have 
been discovered. 

The most important mining district of the county is Lake valley, which is on the eastern slope of the 
Miembres mountains. This range, according to Mr. Gilbert, has a core of Palteozoic limestone, with lava on the 
western slope. The ore bodies occur following the bedding-planes of limestone beds, which dip to the eastward. 
The foot wall is a heavy-bedded bluish-gray limestone, above which are thinly-bedded shaly limestones, carrying 


a Traua. A. I. M. E., Feb., 1882. 





GEOLOGICAL SKETCH OF THE ROCKY MOUNTAIN DIVISION. 103 

fossils of the Waverly group. The ore consists of argentiferous galena and cerussite, with chlorides and 
chloro-broraides of silver in a gangue of red and brown hematite, with some oxide of manganese, and silica in the 
form ot chert. Professor Silliman reports also the occurrence of vanadinite. The deposits apparently resemble in 
their manner of occurrence those of Leadville. Irregular masses and dikes of eruptive rocks are reported also as 
occurring in the region, but their lithological character and direct relation to the ore deposits is not yet definitely 
known. 


GRANT COUNTY. 


Grant county has been the principal mineral producer of the territory, its most important mines being located 
within an area of which Silver City and Fort Bayard form the center. In the Miembres district, on the west slope 
of the Miembres mountains, to the east of Silver City, are argentiferous lead ores in limestones of Palaeozoic 
age. The limestones are fossiliferous, and dip to the eastward; but it is not known whether they correspond to 
those of Lake valley on the east or to those in the neighborhood of Silver City on the west. The deposits follow 
the bedding, having a foot wall of limestone, with shale on the hanging wall. To the north of Silver City is the 
Pinos Altos mountain, which consists, according to Mr. Gilbert, of granite, with porphyry overlapping on one 
side and the lavas of the Diablo range on the other. The veins are quartz veins, carrying both gold and 
silver, having a general north and south strike, and standing at a steep angle. According to the census 
specimens, they occur in both diabase and quartz-porphyry. At Lone mountain, to the south of Silver City, are 
ferruginous deposits, carrying chlorides and sulphides of silver, following the bedding of limestones, which dip to 
the northeast. 

The Burro mountains to the west of Silver City consist, according to Howells, of two bodies of Archaean granite, 
the one covered by heavily-bedded trachytes, the other by Palaeozoic beds dipping to the northeast. In the latter 
occur argentif#ous lead ores, with chlorides and sulphurets of silver. Those in the Chloride Flat district occur 
between limestone beds, and those in the Silver Flat district between an overlying quartz-porphyry or diorite and an 
underlying limestone or dolomite. From the silver-bearing limestones Mr. How'ells obtained characteristic fossils 
of the Cincinnati group. 

In the Santa Rita mountains, according to Mr. Gilbert, argentiferous galena occurs in Carboniferous limestone, 
and veins carrying gold and copper in porphyry. The famous Santa Rita mines are near the crest of the range at 
the contact of the Carboniferous limestone and an overlying porphyry. The Shakspeare or Virginia, district is 
about 25 miles southwest of the Burro mountains, in the Pyramid range, which is made up, according to Mr. Gilbert, 
of basalt and trachyte, overlying an older lava, in which occur the quartz veins. The most prominent of these stand 
up above the weathered surface of the rock, while others less prominent carry argentiferous galena ores with 
chloride and native silver. The country rock most probably belongs to the older or Secondary type of eruptives, 
although Mr. Gilbert describes it as resembling the propylite of v. Richthofen. 


SANTA Ffi COUNTY. 


Mine. 

Country rock and vein. 

Ore and gangue. 

LOS CERRILLOS DISTRICT. 

• 


Ma.rflTin.il Eonanza. 

Supposed to be rhyolite. Vein vertical; strike, N. 38° E.; 2feet 
wide. 

Argentiferous galena and cerussite, with black oxide of manga¬ 
nese and minute crystals of wulfenite (?). 

SILVER BUTTE DISTRICT- ' 

San Pedro and Canon del Agua. 

Quartzite and porphyry on hanging wall; limestono on foot wall. 
No specimens. Deposit with the formation. Strike, N. and S.; 
dip, 10° E.; 30 feet thick. 

Iron-stained quartz, with pyrite, carrying gold; 7 to 8 feet thick on 
hanging wall; underlaid by deposit of azurite, malachite, chryso- 
colla, cuprite, chalcopyrite, and bournonite. No specimens. 


GRANT COUNTY. 


CHLOKIDE FI.AT DISTRICT. 
Bremen. 

Providence. 

lone mountain district. 
Cosette. 

MIEMBRES district. 


Limestone; light-gray and crystalline on hanging wall, dark-blue 
and fine-grained on foot wail. Strike. N. 3° E.; dip, 13° E. De¬ 
posit in irregular bodies on foot wall. 

Dark-blue limetone or dolomite. Vein: strike, N. 40° W.; dip, 
85° E.; average width, 2 feet. 


Dolomitic limestone; light brown, crystalline, and called porphyry, 
on hanging wall; reddish with conchoidal fracture on foot 
wall. Deposits with the bedding. Strike, NW.; dip, 21° E., 
in irregular bodies. 


Commercial 


McGregor 


Naiad Qneen 


Dark carbonaceous shale; foot wall, fossiliferous limestone. No 
specimens. Deposit in irregular pockets with the bedding; 
dip, sTi. 

Dark carbonaceous shale ; foot wall, fossiliferous limestone. No 
specimens. Deposit in irregular pockets with the bedding ; 
dip, SE. 

Dark carbonaceous shale; foot wall, fossiliferous limestone. No 
specimens. Deposit in irregular pockets with the bedding ; 
dip, SE. 


Cerargyrite, argentite, and galena. Gangue: barite, fluorite, and 
argillaceous siate. 

Iron-stained quartz and limestone, carrying chlorides and sulphu¬ 
rets of silver. 


Siliceous hematite, carrying chloride and sulphido of silver. 
Gangue: altered foot wall. 


Argentiferous. No specimens. 


Chlorides and sulphurets of silver, with cerussite and carbonate 
of iron in altered limestone. 

Chlorides and sulphurets of silver and carbonates (?) of iron ; tree 
milling. 


f 






























104 


PRECIOUS METALS. 


GRANT COUNTY—Continued. 


Mine. 

Country rock and vein. 

Ore and gaDgue. 

PINOS ALTOS DISTBICT. 



Langston. 

Mneh altered diabase, called limestone. Vein: strike, N. 15° E.; 
dip, 70° SE. 

Gan gue corussite, chlorides, and sulphides of silver carrying 
gold. 

Mina Grande. 

Called quartzless granite, or trachyte. No specimens. Vein: 
strike, N. and S.; dip, 80° E.; 2 feet wide. 

Auriferons quartz, with chlorides and sulphides of silver. No 
specimens. 

Ohio. 

Decomposed quartz-porphyry. Vein: strike, N. and S.; dip, E.; 

4 1'eet wide. 

Galena, chalcopyrite, with harite in quartz, carrying gold and 
silver. 

Pacific No. 2. 

SILVKB FLAT DISTRICT. 

Probably diabase. Vein: strike, N. and S.; dip, 75° E.; 2 feet wide. 

Mixture of barite, quartz, pyrite, and galena, carrying gold and 
silver. 

Massachusetts and New Mex¬ 
ico. 

Hanging wall light-colored quartz-porphyry j foot wall dark 
dolomite. Deposit with the bedding. Strike, N. 32° W.; dip, 
85° E. j up to 15 feet thick. 

Chlorides and sulphides of silver, with quartz and calcite. 

Sherman. 

Hanging wall altered, eruptive rock, possibly diorite; foot wall 
dark brown dolomite. Deposit with the bedding. Strike, N. 
and S.; dip, 15° E. 

Galena, with chloride and sulphide of silver. 
























■ 






















-■ ' 

'• • 








' 

■ 




















• ' 

’■ •• ■ ■ • 

■ 

■ ' - V ■ .. 













. ■ 







t .... ••• ■ ■ •• 

- 





286 


PRECIOUS METALS. 


C h apter VI.—LEAD SMELTING AT LEADVILLE, COLORADO. 

By S. F. Emmons. 


PLANT. 

Introductory. —Although a very large amount of technical data on the various smelting works of the West 
was collected by the census experts, they were not found sufficiently complete to serve as the sole basis for a 
detailed description of the processes employed; nor do these works in general, as far as they are open to public 
inspection, present any features which are unusual or new to metallurgical science. At Leadville, however, where 
the numerous smelting establishments produce annually about 815,000,000 worth of argentiferous lead bullion, 
metallurgists have necessarily acquired an unusual amount of practical experience in the conduct of the operations 
of lead smelting and in the management of the business connected therewith. It has therefore been judged 
expedient to present a succinct account of the natural and economical conditions of smelting at this point, of the 
character of the plant, and of the processes employed. For this purpose recourse has been had to the MS. of a 
report by Mr. A. Guyard on the lead smelting of Leadville, which is to appear as an appendix to a monograph 
on the geology and mining industry of that district. An abstract of this report has been made by Mr. W. F. 
Hillebrand, and is supplemented by data obtained from census material and by himself and the writer personally, 
which appears in the following pages. In this the chemical investigations and calculations made by Mr. Guyard 
have been freely used, and the two illustrations which accompany it are taken from his plates.; but all discussion 
as to the fitness or unfitness of methods employed, or of theoretical questions arising therefrom, has been avoided. 

Topographical conditions. —An important condition in the disposition of smelting works, as well as of 
quartz-mills and other reduction works, is that the force of gravity may be used as an aid in handling the material 
to be treated, which is generally of a heavy and bulky nature. To such a disposition the surface character of the 
Leadville region is admirably suited by nature. The town itself is situated on a gently sloping mesa included 
between Evans gulch on the north and California gulch on the south, at the western base of the foot-hills of the 
Mosquito range, iu which its ores occur. Along the high banks, which rise from the bottom of either of these 
gulches to the comparatively flat surface of the mesa, and at a sufficient elevation to allow room for the slag dumps 
below them, are located the various smelting works. They are thus situated so that from the mines an equally 
favorable grade leads either to the upper or the lower portion of the works, and the railroad which follows the 
surface of the mesa sends its branches on the level of or above the charging floor, and thus delivers its freight of 
fuel or of ore where it may desceud through the various stages of the process until the final product, the bars 
of bullion, is obtained. 

Disposition of the plant. —No less than sixteen smelting works have been built at Leadville in the few 
years that have elapsed since its mines were opened. Of these, however, a number have been closed, some 
temporarily, others permanently. The general plan in these works is that adopted elsewhere, and involves the 
occupation of two principal floors. The lower of these floors is at such a height above the adjoining valley 
bottom as to afford a convenient opportunity for dumping slag and other waste. On this floor the furnaces are 
built, and room is also commonly provided for the blower and the engine by which it is actuated. The furnaces 
are usually placed in a row within a single inclosure, but sometimes they have a wall intervening between them. 
The upper floor is on a level with the feeding-door of the furnaces, from 12 to 14 feet above the lower, and affords 
space for ore-bins, fluxes, mixing-beds, and the operations connected with charging the furnaces, such as crushing 
and sampling. When the slope of the ground is great, however, the storage bins for ore and fuel are sometimes 
placed at a still higher level, with passages for wagons between. One roof generally covers the whole establishment, 
with the exception of the offices, laboratory, and scales, which commonly occup}’ - detached buildings. 

Furnaces. —Shaft furnaces only are employed in Leadville. Of these two varieties were in use during the 
census year, the one presenting a circular horizontal cross-section, sometimes called the Piltz furnace, while" the 
other is rectangular; but in 1882 the latter had entirely replaced the former. While the circular section presents 
advantages in the regularity of the descent of the charges, it is more expensive in construction, and the diameter 
of the hearth is limited by the strength ofjthe blast; indeed, with any ordinary blowing-engine a round furnace can 
be successfully worked only when it is of very moderate dimensions. The rectaugular or Rasehette furnace, on the 
other hand, may be constructed with a width at the tuyeres corresponding to the strength of the blast-engines, and 
the production may be increased by increasing the length of the cross-section. The horizontal elongation of the 
furnace has its limits, indeed, as has been proved by the history of the rectaugular Rasehette furnaces in Europe, 
but the capacity may nevertheless be increased considerably above that of a circular furnace of similar construction 
without deleterious effects upon the working. In lead smelting, and especially in smelting argentiferous lead ores, 




Department of the Interior 


Plate T 


Tenth Census of the United States 



EtLEVATICH 


Wroufhl Iron 


Cast Tron 


Fire Brick 


Scale;! inch, to 6 feet 


Fia. 2. SECTION ON a 


RECTANGULAR FURNACE 












































































































































































































































































































































































































































































































































LEAD SMELTING AT LEADVILLE, COLORADO. 


287 


it is very undesirable to employ the high pressure blasts required by a circular furnace of large diameter, since the 
higher temperatures which result promote the production of fumes which are only imperfectly recovered and are 
always difficult of treatment. 

The rectangular and the round furnaces of Leadville are constructed on the same general plan so far as height, 
method of support, water-jackets, tuyeres, etc., are concerned, but the sizes adopted vary greatly, the limits of 
capacity being from 15 to 40 tons in twenty-four hours. 

Plate I, Fig. 1, represents a rectangular furnace in elevation drawn to a scale of 0 feet to the iucli, and Fig. 2 
the same furnace in horizontal section at the tuyere level. Fig. 3 shows a vertical section of the same furnace on its 
longer diameter, and Fig. 4 a horizontal section at the charging-doors. The masonry shaft (C) rests upon a cast-iron 
plate (0), supported by pillars (P), in order that there may be no unnecessary weight on the lower portion of the 
furuace. The walls for some distance above and below the tuyeres are formed of sectional water-jackets ( B ), 
constructed of cast or wrought irou or of steel. In the furnace illustrated the water-jackets are twelve in number^ 
firmly bolted together and provided with openings for the insertion of the tuyeres (N). A cold water pipe (M) 
runs around the furnace above the water-jackets, and water is admitted to each of them by a faucet ( Y ). Outlets 
( Af ') for the hot water and gutters ( T) for its removal are also shown iu the illustrations. The interval (b) between 
the water-jackets and the plate on which the shaft of the furnace rests is filled with fire-brick, which can be readily 
removed iu case of necessity. The lower ends of the water-jacket rest upon the hearth (X). This consists of cast- 
iron plates (a) bolted together and lined with a thick coating of fire-brick or of “ steep” (brasque), a mixture of fire¬ 
clay and coke-dust, either in equal parts, or in the proportion of two of the former to one of the latter. The usual 
form of the hearth is shown in the illustrations; this, however, is modified'in detail, according to the working of the 
furnace and the judgment of the manager or smelter, changes in it involving no modification of the iron plates. 

The hearth plates include also the lead well L and the so-called “siphon tap”. A similar device was long ago 
applied to the small charcoal-iron blast-furnaces of Silesia, to permit of the manufacture of castings without 
tapping the furnaces; it was not successful, however, the iron chilling too rapidly for the object in view, owing to 
its high melting point. This arrangement was introduced into lead smelting in Eureka, Nevada, by Mr. Albert 
Arents with great success, and has since been widely adopted both in this country and abroad. The lead rises 
through the oblique tap-hole L‘ shown in Fig. 1 to the same level in the well which it occupied in the furnace, and can 
be baled into the molds at leisure, and without the disturbance of the furnace-working incident to the old method 
of tapping at long intervals. 

At the end of the furnace just above the hearth an opening (F) is left in the water-jacket to facilitate the tapping 
of slag. This opening is filled with clay, in which a hole can be pierced when required, allowing the slag to pass 
through an inclined gutter ( U), shown in the illustrations,, iuto a slag-buggy. A hood ( IF) is generally placed over the 
tapping-hole to draw off the fumes emitted during the tapping. The number of tuyeres varies with the size of 
the furnace, depending mainly on the length of tbe cross-section. A tuyere is always placed at the end of the 
furnace opposite the slag-tap, and sometimes also above it; this last, however, is somewhat in the way, and is 
often omitted. A sliding valve (/) at the elbow of the nozzle admits of the inspection of the interior of the furnace. 
Tbe tuyeres are connected with the main blast-pipe (I) by canvas hose ( K ), the flexibility of which permits their 
withdrawal from the furnace when necessary. This convenient device is, of course, applicable ouly when cold air 
is supplied to the furnace, as is almost invariably the case in lead smelting. Feed-openings (II) on the upper floor are 
closed by sliding doors (8). The furnace terminates upward in a short chimney (E) and may, in case of need, be run 
without the dust-chambers, with which it is connected by a flue ( F ) indicated in the illustration. 

As an example of recent construction, the furnaces in the works of Eddy, James & Grant, at Denver, may be 
cited. There are eight of these furnaces of the same pattern, all built iu the spring of 1882. The height to the 
charging-door is 18 feet; the dimensions 3 feet below the charging-door are GO by 102 inches; at the top of the 
jackets, 48 by 924 inches, and at the tuyere level, 36 by 804 inches. Each furnace has ten tuyeres, four on each 
side and one at each end. The capacity of each is about 30 tons. The waste gases and fumes are drawn from all 
these furnaces at a point below the charging-doors into large dust-chambers connecting with a single stack—a very 
convenient arrangement so far as the comfort of the workmen is concerned; whether it is accompanied by any ill 
effect upon the working of the ore is regarded as uncertain, but each furnace is provided with an independent stack, 
to be used in tbe event of its proving desirable to return to the ordinary practice. 

Plate II shows a furnace with a circular horizontal section on the same scale as the rectangular furnace 
illustrated on Plate I, and a comparison will show that the general principles governing tbe construction are the 
same in both. A main point of difference is iu the anchoring, which in the square furnace is necessarily effected 
by bars (CJ), while the same object is more conveniently attained, when the section is circular, by a shell of sheet 
iron ( J) composed of plates about a quarter of an inch in thickness. Tbe diameter of round furnaces at the tuyere 
level is from 33 to 48 inches, and the capacity varies with this dimension. 

Dust-chambers. —The appliances for catching flue-dust in the Leadville smelting works are generally very 
imperfect, but tbe reproach does not apply to Leadville alone, for, however extensive the system employed elsewhere, 
it fails to accomplish its purpose completely. It is said that some English lead works have dust-chambers no less 
than 5 miles in length, and yet fail to recover all the dust carried from the furnaces; some of the Leadville works, 
however, make no attempt to collect the flue-dust, a practice unworthy of imitation. The ordinary provision 


288 


PRECIOUS METALS. 


consists of brick chambers on or below the charging-floor, either divided into sections by walls and curtains or 
not. One such chamber is 75 feet long, 25 feet wide, and 15 feet in height, and another of the same length is only 
4 feet wide and G feet high. The dust chambers are sometimes built of iron instead of brick, and the circuitous 
direction given to the current by the interposition of walls and curtains in brick chambers is then often obtained by 
the use of adjoining vertical cylinders, the air and fumes entering the bottom of one and the top of the next. 

Blast-engines.— The blowing engines employed are most commonly of the Baker rotary pattern, though at 
one establishment the Root blower is in use. The pressure of the blast furnished by these blowers varies from 
half an inch to 14 inches of mercury, or say from one-fourth to three-fourths of a pound per square inch, the most 
usual tension being 1 inch of mercury, or about half a pound per square inch. Where several blowers are employed 
in furnishing blasts to more than one furnace the pressure is equalized, and the probability of an interference with 
the work through the stoppage of a blower is decreased by connecting them all with the same main blast-pipe. 

The iron work of the furnaces is sometimes made by Denver firms, but usually the entire plant is ordered 
from the East. 

Bartlett filter.— An experiment was made at one of the works with this arrangement for collecting 
flue-dust which gave some interesting results. The following is condensed from Mr. Guyard’s description: 

The stack of one of the square furnaces was connected with a Sturtevant fan by means of a sheet-iron flue, 
through which the fumes were drawn from the furnace and blown through a sheet-iron pipe 150 feet in length, 
which was connected, by means of two branch pipes, with two boxes of thin sheet iron. The dust was collected in 
the sheet-iron pipe as in an ordinary flue. Each branch pipe was provided with a damper, or valve, similar to those 
used in stovepipes, so that the fumes could be distributed to one or both of the boxes at pleasure. Each box 
consisted of a dust-chamber and a fireplace, the former being provided with sliding doors, placed at either extremity, 
and the fireplace with doors in frout and sheet-iron pipes at the back, communicating with a stack. At the top of 
each of the dust-chambers were twenty-eight apertures, to each of which was fastened a cloth bag, 30 feet high, 
suspended to the beams of a light wooden structure, in which the apparatus was inclosed, and which was provided 
with very large openings for ventilation. When the apparatus is at work the fumes blown in distribute themselves 
in the dust-chambers and ascend the cloth bags, through which they are filtered. The gases come out perfectly 
colorless and free from any lead dust or even soot. The wind entering freely through the apertures of the building 
shakes the bags, and the dust with which they are charged falls back into the dust-chambers. When a sufficient 
quantity of this dust has been accumulated, the doors connecting with the fireplace are opened and a light 
wood fire is kindled. The soot soon catches fire aud burns off, leaving the dust white. During a run of five days 
3,030 pounds of calcined dust were caught in a Bartlett filter from one furnace. The experiment was not entirely 
satisfactory, owing to defects in the manner in which it was carried out; but the defect was one of arrangement, 
and by no means inherent in the filter. The furnace was worked without closing the feed-hole, as with an ordinary 
dust-chamber. The Sturtevant fan consequently drew in as much air as smoke, so that the chamber of the furnace 
had to be left half open, and about half the smoke escaped directly into the open air. The use of this arrangement 
was abandoned by the owners of the works partly on account of the expense involved and partly, as stated by 
them, on account of the large percentage of arsenic (15 to 20 per cent.) in the condensed matter and its low tenor 
in silver. As Mr. Guyard, in his analysis of this substance, found extremely little arsenic and much lead, chiefly 
combined with phosphoric acid, chlorine, and bromine, it is difficult to imagine on what ground the presence of 
arsenic in such quantity could be inferred. Mr. Guyard’s analysis is supported by the fact that arsenic is present 
to but small extent throughout the district, while phosphoric acid exists in large quantities in many of the ores. 

RAW MATERIAL. 

Okes.— The ores of Leadville are remarkably pure argentiferous lead ores. They are locally divided into two 
general classes: the “sand carbonates”, which are loose, sandy masses of carbonate of lead with chloride of silver, 
and the “hard carbonates”, which are masses of porous siliceous material with a varying proportion of hydrated 
oxides of iron and manganese, carrying carbonates of lead and chlorides of silver, and sometimes containing a 
considerable proportion of unaltered argentiferous galena. As a rule, with the exception of mechanical mixtures of 
clay and varying proportions of iron and silica, they contain but few foreign ingredients. Intimately associated 
with the carbonates is generally a little pyromorphite or chloro-phosphate of lead, amounting in one exceptional 
case to 10 and in another to 30 per cent, of the whole. Sulphate of lead also occurs in small quantity, with small 

aud variable amounts of oxidized compounds of copper, arsenic, antimony, and manganese. The latter is often 

» 

abundant, and is associated with or replaces iron oxide. Ores which are rich in manganese are generally poor in 
silver. The galena is frequently covered by a coating of carbonate showing clearly the alteration of the sulphide, 
first to sulphate, and then to carbonate. In some few mines bismuth and vanadium ores have been found. But a 
small proportion of the ores smelted is furnished by districts outside of Leadville. Of this the greater part comes 
from Ten-Mile district, in Summit county, and especially from the Robinson mine, whose deposits carry much pyrite 
and ziucblende. The silver in the oxidized ores is preseut in combination with chlorine, bromine, and iodine, 
either as chloride, chloro-bromide, or chloro-bromo-iodide, as the analyses on page 289 of specimens from several 
mines made in the laboratory of the United States geological survey at Denver show. 


\ 




Department of the Interior. 


Plate II. 


Tenth Census of the United States. 




FCg 3 SECTION ON 


Cast li on 


U’rouiM Iron 


Clay 


Scale: l inch to 6 feet oi i>72 


FEET 

f 


IIEIEKS 


Sleep 


Fig. 2. SECTION ON ftp. 


a - 


CIRCULAR FURNACE 




































































































































































































































































































LEAD SMELTING AT LEADVILLE, COLORADO. 


289 


1 

R. E. Lee mine. 

Amie mine. 

Big Pittsburgh 1 
mine. 

Chloride of silver. . 

21. 589 

15.755 

■■ ■ ■ 1 

99.905 i 

Bromide of silver. 

77. 986 

84. 091 

None. | 

Iodide of silver.... - . 

0.425 

0.154 

0.035 j 


Large masses of chloride of silver, or horn-silver, have been found, and on several occasions tons of ore have 
been taken from the E. E. Lee miue assaying from 8,000 to 15,000 ounces of silver to the ton and almost entirely 
free from lead. According to Mr. Guyard, sulphide of silver is sometimes present in small quantity. 

The Leadville ores in geueral contain little or no gold, its presence not being easily detected in the ore itself, 
but only being shown in the final product. The average daily output of the mines in 1880 is placed by Mr. Guyard at 
from 700 to 800 tons, and the total smelting capacity of the.furnaces at 700 tons per diem. 

Fluxes. —The fluxes used in Leadville are limestone and hematite. During the census year the limestone 
used was the blue dolomitic limestone (Lower Carboniferous), in which the Leadville ores occur, taken either from 
open quarries or from dead-work in some of the mines. In the latter case it often carried a small percentage of silver. 
Experiments showed that dolomite was a less favorable flux than pure carbonate of lime, and since the advent of 
the railroad limestone has been obtained from the beds of the Colorado Cretaceous formation at Canon City, 117 
miles distant, and more recently still from a bed in the Upper Coal Measures at Eobinson, 16 miles distant by rail, 
where it costs $3 per ton f. o. b. Eed hematite iron ore was at first exclusively used as a flux, being principally 
obtained from the Breece iron mine, where it occurs in large masses between the White and the Gray porphyry, and 
it is said to carry a small percentage of silver. More recently it has been the practice in many smelters to use the 
limonite which had collected on the dumps of the various mines, and which also carries a small percentage of silver. 
In many cases the ores themselves are so ferruginous that but little additional iron is required. 

Fuel. —The fuels used are coke and charcoal. Previous to the advent of the railroad coke was scarce and' 
dear, having to be brought 30 to 150 miles by ox or mule teams; hence charcoal was much more largely used 
than at present. This is furnished by the forests of spruce covering the neighboring mountain slopes. The charcoal 
produced from these woods varies greatly in quality, according to whether it has been burned in pits or in kilns. The 
pit-charcoal made in the neighborhood of Leadville is said to contain 2.5 per cent, of ash; a sample of kiln charcoal 
was found by Mr. Guyard to contain 1.62 per cent, of ash. One hundred and forty-two and one-half bushels of 
charcoal make 1 ton, the bushel weighing 14 pounds. 

Coke.— The cokes used are brought from El IVJoro, in the southern part of the state, by the Denver and Eio 
Grande railroad, and from Como, in the South Park, by the Denver, South Park, and Pacific railroad. These 
cokes are made from coals of the Lignitic or Upper Cretaceous formation, and contain, according to determinations 
made at the smelting works of Messrs. Billings & Eilers, 22 per cent, of ash for the El Moro and 9£ per cent, of 
ash for the South Park coke. The composition of the ash of the El Moro coke is represented as being 84£ per cent, 
silica, 7.1 per cent, peroxide of iron, and 8.4 per cent, alumina, lime, etc. The ash of the South Park coke shows 
29.1 per cent, silica, 47.8 per cent, peroxide of iron, and 23.1 per cent, alumina, lime, etc. About 40 pounds of coke 

make one bushel; hence, 50 bushels make one ton. 

7 • 

Ore buying. —Ore is purchased either directly from the mines themselves for cash or from sampling works, 
which either buy from the mines or act as their agents. Various considerations affect the price paid. From the assay 
value of the ore in silver a certain percentage is deducted for loss in smelting, which varies according to the nature 
of the ore, whether siliceous, ferruginous, or sulphureted, or according to a special arrangement made between the 
mine owners and the smelter owners. A further variable charge is made for cost of treatment, which is dependent 
on the nature of the ore and its tenor in lead. As a general rule, in regard to oxidized ores, the charge for treatment 
is lower the larger the percentage of lead they contain. When this tenor is between 5 and 30 per cent, the lead is 
paid for at from 15 to 45 cents a unit of 20 pounds; the higher the percentage of lead the higher the price paid per 
unit. When the ore contains less than a certain percentage of lead, which varies with the quality of the ore, the 
mine owner receives no remuneration for the lead contained in his ore, however rich it may be in silver. The 
following table gives a specimen of the rates charged for treatment of the ores of some of the best-known mines, 
the deduction made for loss of silver, and the price paid for each unit of lead above this certain percentage : 


Name of mine. 

Deduction 
for loss of 
silver 

in smelting. 

Cost of treat¬ 
ment per 
ton of ore. 

Price of lead 
per unit of 
20 pounds. 

Amie. 

Per cent. 

10 

$25 

$0 25 

Chrysolite. 

5 

20 

25 

Dunkin. 

5 

22 

25 

Carbonate. 

Vi 

20 

25 

Evening Star. 

Vi 

28 

25 

Morning Star. 

5 

15 

30 

Iron. 

5 

18 

30 

Tucson. 

6 

21 

25 


YOL 13-19 










































290 


PRECIOUS METALS. 


These figures vary from month to month unless a time contract lias been entered into, and are governed by 
the market quotations of silver and lead at New York and the prices of coke, charcoal, and fluxes at Leadville. 
Gold, when present in excess of one-tenth of an ounce to the ton, is paid for at the rate of $18 per ounce. The 
transportation of ore from the mines to the sampling or smelting works is paid for by the smelters at the rate of 
$1 to $1 85 per ton. 

Sampling.— When the ore arrives at the sampling works, it is weighed in the wagon on scales generally 
occupying a detached building. It is then thrown into bins or piles in the open yard, every tenth shovelful as a 
rule being put into a wheelbarrow. The sample thus obtained is spread out on the. sampling floor, and in the case 
of a sand ore is worked up directly to obtain a thorough mixture. Hard ores are first passed through Cornish rolls. 
When the ore is thoroughly mixed, it is repeatedly quartered till a sample convenient for drying has been obtained. 
After drying it is further crushed, mixed, and quartered, and a portion is then ground on the bucking plate by 
the bucker ( a ) until it passes through a sieve of 70 to 80 meshes to the linear inch. The sample is then divided 
into three portions, one of which is assayed at the smelter, and a second at the mine or by a public assayer who may 
be employed by the mine. If the results of the two assays agree closely, a mean is generally taken as the true 
value of the load ; otherwise the third portion is sent for control to a third independent assayer. Sand ores requirfe 
no crushing before charging into the furnace. For hard ores, slags, fluxes, etc., Blake, and occasionally Alden 
crushers, driven by steam-power, are employed. 

Smelting charges.— The construction of ore-beds is carried on to a considerable extent at both smelting and 
sampling works. These beds average from 1G0 to 180 tons each in weight, and contain approximately equal parts 
(20 to 25 per cent.) of metallic lead, metallic iron, and silica, of which the proportion of lead is subject to the 
greatest fluctuation. The proportion of silver to lead is 1 ounce to about G or 8 pounds. Snlphureted ores are 
not roasted, but are thrown directly into the furnace, and are mixed in-small quantities with the oxidized ores. 

The charges vary so greatly in composition at the different smelters that it is hardly possible to give that of 
an average one. At first the aim seems to have been to produce a normal singulo silicate slag, but a change has 
been gradually taking place to slags of a slightly more acid character, containing from 32 to 3G per cent, of silica. 
At one smelter the aim is said to have been to produce a slag in which the proportion of earthy base to metallic 
base should be as one to two, or to some even number. The following examples of different charges are taken from 
Mr. Guyard’s report as specimens of their variable! character: 


ORE: 

Ore-bed mixture . 

Unmixed ore. 

Lead scraps. 

Flux: 

Dolomite. 

Hematite. 

Blag. 

Fuel: • 

Charcoal. 

Cote.. 


Total weight of charge.. 


I. 


Founds. 

100 

50 


10 

10 

30 


15 

20 


150 


50 


35 

235 


H. 


Pounds. 

200 

300 

10 


50 

150 


80 

60 


510 


200 


140 


m. 


Pounds. 

123 

183 


90 

7 

60 


50 

50 


850 


306 

157 

100 

563 


IV. 


Pounds. 

500 

200 


80 

170 

80 


95 

65 


700 


330 


160 


L 190 


V. 


62 

80 


80 

60 


Pounds. 
645 


645 


142 


140 


927 


The proportions of charcoal and coke in the fuel vary, according to supply and cost and from other 
considerations, within the limits of three parts of the one to four of the other. 

The table on page 201 gives the calculations made by Mr. Guyard from data obtained for the census year in eight 
of the principal smelting works of Leadville: First, the average proportion of flux to 100 parts of ore; second, the 
proportion of fuel to 100 parts of ore; third, the proportion of fuel to 100 parts of smelting charge. In the fourth 
rubric is given the number of tons smelted per twenty-four hours in each of these works. From these data he 
calculates the relation of actual to nominal smelting capacity as varying from 2G to 80 per cent. Furnace III is 
regarded as fulfilling most nearly theoretically perfect conditions. 


a The bucking plate in ordinary use in assay offices in the West is a cast-iron plate measuring 2 by H feet, with flanges on the long 
side rising half an inch above the surface; the latter is planed down, but not polished. The bucker or rubber is a rectangular piece of cast 
iron 7 by 5 inches, and from 1 to inches thick. On the upper surface is a socket for a long wooden handle, aud the lower surface is 
curved (a portion of a large cylindrical surface) so that, as the operator pushes it to aud fro on tho plate to pulverize the ore, a slight 
rocking motion may be given at the samo time, which brings the particles under the bucker instead of pushing them before it. 


























































LEAD SMELTING AT LEADVILLE, COLORADO. 


291 



I. 

H. 

III. 

iv'. 

V. 

VI. 

VII. ! VIII. 

Proportion of flux to 100 parts ore. 

25.00 

39.0 

42. 0 

24.0 

28.8 

40. C 

33.5 | 31.70 

Proportion of fuel to 100 parts ore. 

45.33 

33.0 

33.8 

18.5 

23.0 

40.2 

25. 0 25. 54 

Proportion of fuel to 100 parts charges. 

30. 00 

23.5 

23.7 

15.0 

19.3 

31.5 

18.5 18.00 

Tons of ore smelted per twenty-four hours_ 

28. 00 

104.0 

51.0 

11.5 

23.0 

15.9 

69.5 32.50 i 

i 


The proportions obtained by Mr. Guyard as an average for the entire camp during the census year are: 

32.83 parts fuel to 100 parts ore. 

23.G5 parts fuel to 100 parts charges. 

ITe calculates that 88 per eent.*of the lead in the ore is extracted as bullion by direct smelting, the remainder 
going into the slag and escaping up the stack; also that 1£ parts of fuel are required for each unit by weight of 
bullion produced. 

In the following table Mr. Guyard has calculated witli regard to the same furnaces shown in the preceding 
table: First, percentage of lead extracted in smelting in the form of bullion; second, the percentage of silver 
extracted; third, the average charges for smelting per ton of ore at each establishment; fourth, the cost to the 
smelter of treating each ton of ore; fifth, the average assay of slags in ounces of silver per ton; sixth, the average 
assay of flue-dust in ounces of silver per ton: 



I. 

II. 

HI. 

IV. 

V. 

YI. 

VII. 

VIII. 

Percentage of lead extracted in smelting. 

85 to 88 

80 to 91 

88.0 

85 to 95 

85 to 90 

90 to 93 

87.0 

90.0 

Percentage of silver extracted in smelting. 

100 

95 to 97 

97.0 

88 to 95 

95.0 

97.0 

98.5 

97.5 

Charges for smelting per ton of ore. 

$15 to $30 

$15 to $30 

$15 to $30 

$12 to $25 

$10 to $30 

$15 to $30 

$15 to $30 

$15 to $30 

Cost for smelting per ton of ore. 

$12 to $18 

$18 to $23 

$10 to $15 

$13 to $1G 

$15 to $18 

$13 

$13 08 

$15 

Average assay of slags in ounces of silver. 

2 

4 

0. 5 

1.5 

1.5 

1.5 

1.5 

4.0 

Average assay of tine-dust in ounces of silver. 

30 

37 

30.0 

35.0 

35.0 

30.0 

30.0 

37.0 


The above table shows only the conditions which obtained during the year ending June 1, 1880. These have 
been varied since that time by a general reduction of the smelting charges, owing to competition and to the 
cheapening of supplies, and also by the reduced tenor of the ore in silver. The proportion of sulpliureted over 
oxidized ores will also probably increase as time goes on. 


GENERAL SMELTING OPERATIONS. 


Blowing-in of furnaces. —The furnace is first dried by means of a slow charcoal or wood fire, whose 
temperature increases gradually for several days. When the drying is completed, the fire is allowed to burn out 
and the furnace left to cool. The crucible is then lined with steep or brasque; tamping, a simple lining of fire-clay, 
is sometimes put upon the dam, siphon, and siphon-tap. The furnace is then filled to the feed-hole with charcoal, 
the tuyere-holes, tympstone, and stack-damper being left open to create a draught. The charcoal gradually 
becomes incandescent to the very throat. When this zone has reached a low red heat the blowing-in begins. The 
tuyere holes of the water-jacket, with the exception of from two to four of those nearest the front, are sealed with 
plugs of clay, and the wind-bags of the corresponding tuyeres are tied up with strings. Tuyeres are inserted in the 
holes left open; the tympstone is set in, and the blast then turned on at full pressure. A long flame issues from 
the siphon-tap, and the fire is kept steadily up until the lead-well becomes red hot. The remaining tuyere-holes are 
then opened and all the tuyeres are set in. The blast is regulated to the normal pressure, and the furnace is now 
ready for the filling of the crucible. 

Filling of the crucible. —Bars of bullion kept in reserve for this purpose, in amount varying from 4 to 
12 tons, according to capacity, are thrown in at the feed-door with more fuel, the proportion being three bars of 
bullion (300 pounds) to eight shovels of charcoal, or about 14 per cent, of fuel. From 100 to 150 bushels of charcoal, 
according to the capacity of the furnace, are consumed during the blowing-in. When molten lead makes its 
appearance in the lead-well, a few' pieces of live charcoal are placed on it to prevent it from cooling, and the 


furnace is ready for charging. 

Charging of the furnace. —Old slags are first of all thrown into the furnace as a test of its temperature, 
which is not ready until the slag is perfectly fluid. The head smelter or his assistant opens the tap-hole in the 
tympstone from time to time to observe their degree of fluidity, and the regular charging begins only when they run 
quite freely. The charges are disposed on the inside of the furnace next to the walls, a depression being left in the 
center for the fuel. This is the mode of charging generally adopted, but there are variations in the manner of 
mixing the materials forming the smelting charges. At some of the smelting works fuel is first thrown in, then old 
slags, above these the fluxes, and then the ore; at others fuel is mixed with the old slags and fluxes with the ores. 
The mode of proceeding generally adopted, how ever, is to mix slags, fluxes, and ore together and keep the fuel 




























































292 


PRECIOUS METALS. 


separate. At the most successful establishment the method of mixing fuels and old slags on the one band and 
fluxes and ore on the other prevails. In either case the distribution of the materials in the furnace is the same; i. e., 
fuel is thrown in the center and the charge is distributed around it. 

Tapping of slags. —The tapping of slag commences as soon as the furnace is in regular operation, and 
occurs generally every fifteen or twenty minutes, although a few works have adopted the method of continuous flow 
from the tap-hole. The tap-hole is closed by a lump of clay at the end of an iron tapping-rod. The slag is caught 
directly in a slag-buggy or conical cast iron pot mounted on wheels, and is either allowed to solidify entirely in 
the pot and then thrown out and broken up, or it is wheeled to the edge of the slag fieap and tipped over so that it 
runs in a half liquid state down the sides of the dump. A single smelter adopts the plan of allowing the slag to 
solidify partially in the pot, and of then making holes through the hardened eryst and tipping the pot over so that 
the still molten material runs out, leaving a shell over 2 inches thick. This shell is easily broken up for re-smelting, 
it having been found that it is a little richer in silver than the center. Slag samples for assay are taken two or 
three times a day from the stream in the slag gutter, and their specific gravity and contents in lead and silver are 
determined in the assay office. Any speiss or matte that may be formed is run into the slag-pot with the slag, and 
iseither thrown out with the latter upon the dump, or, after cooliug, is detached from the slag and preserved separately. 
The proportion of speiss and matte at Leadville is generally very small. 

Ladling of bullion. —As often as necessary the bullion is dipped out of the lead-wells with wrought-iron 
ladles and poured into cast-iron molds. At a single smelter a different method obtains. The bullion is tapped 
periodically from an opening in the clay lining of the lead-well into an iron pot mounted on a small stove, in which 
a light fire is kept burning. From this pot it is ladled into the molds. The advantages of this method are that 
the surface of the lead in the well is kept covered. The lead is therefore hotter, and the passage into the crucible is 
more readily cleaned. Moreover, the lead being drawn from below, the surface is free from skimmings, and the 
bars are smoother and cleaner. 

The bars of bullion are then sampled, weighed, and marked. The sampling is done by taking with a scoop- 
chisel a piece from the top and a piece from the bottom of each bar. The samples from 200 bars, or 10 tons, which 
constitute a car-load, are sent to the assay office, where they are melted together and cast into a small bar, from 
which pieces are taken for an assay. 

Control of smelting operations. —From time to time the siphon-tap has to be cleared by the insertion 
of a curved iron rod, about 2 inches thick, previously heated to redness at the curved end. 

The tuyeres must be watched from the sliding valve, and when dark rings of chilled slag are observed around 
them they are removed by iron rods inserted through the tuyere, and the temperature is raised by the addition of 
more fuel or by a reduction in the proportion of charge. 

The water-jackets require constant watching, iu order that the temperature of the water issuing from them 
may be kept as nearly as possible at from 50° to 00° C. 

The blast also requires constant attention and regulating, the pressure being increased or diminished as the 
condition of the furnace, determined by observation from the tuyeres, may demand. 

If semi-fluid slags or raw ore form accretions, which do not disappear by an increase of the temperature, the 
blast must be shut off, the tympstone removed, and the hearth cleaned by means of bars and sledges; after which 
a little fuel is thrown into the hearth, the tympstone is replaced, and the blast is turned on again. At one period ores 
rich in lead were scarce at Leadville, and the charges generally contained much less than the normal 20 to 25 per 
cent, of lead. The running of the furnace became, in consequence, a much more difficult matter, and the formation 
of obstructions of various kinds was of frequent occurrence. 

When accretions form on the walls of the shaft, it is necessary to “bar it out” once in twenty-four hours, or 
once per shift, as the case may be. To accomplish this charging is interrupted until the contents of the furnace 
descend to the level of the accretion. The blast is then turned off, a long chisel-pointed bar is introduced into the 
feeding hole of the furnace, aud, being inserted between the accretion and the furnace wall, is struck with sledge¬ 
hammers until the accretion is detached, when the blast is turned on again and the charging resumed. 

The Leadville furnaces are generally run with a dark top; i. e., the zone at the throat is so dark that no flames 
issue from it, and only a black smoke is seen ascending the chimney. This appearance is an indication that the 
furnace is running properly. 

Smelting of flue- and chamber-dust. —Flue- and chamber-dust are mixed in general with lime, and the 
mixture may or may not be molded into bricks. It is then spread over the ore beds, so that a little of the flue-dust 
enters into the composition of the smelting charges. 

Blowing-out of furnace. —This takes place when the furnace needs repairing, or when au accident, 
interfering with the regular working of the furnace, has occurred. It is done by suspending the charges and 
continuing the blast until the whole contents of the furnace are molten. The charge soon burns with a bright top, 
and the furnace emits torrents of heavy white fumes. When the whole charge has reached the level of the 
tuyeres the furnace is emptied of its fluid contents, first from the tap-hole, then the breast is removed, and the 
bullion is taken out of the crucible. » 

Length of run. —The smelting campaigns are seldom less than three weeks, and often reach six, eight, and 
even thirteen months. 


t 


LEAD SMELTING AT LEADVILLE, COLORADO. 


293 


FURNACE PRODUCTS. 

Bullion.— The bullion of Leadville is generally very pure, its constituents other than lead and silver, though 
numerous, being present in very small quantity. The character of these impurities is shown in the following 
analyses made by Mr. Guyard, I being bullion from the La Plata smelter, II being a mixture of equal parts of 
bullion from nine different smelters: 



I. 

n. 

Lead (by difference). 

99. 0798210 

98. 492379 

Silver. 

0.6112445 

0. 793417 

Gold. 

0. 0000888 

0.000891 

Copper. 

0.0479100 

0. 071450 

Tin. 

A faint trace. 

0. 000897 

Bismuth. 

A faint trace. 

0.011791 

Arsenic. 

0.0391365 

0.219528 

Antimony. 

0.2138940 

0. 347881 

Iron. 

0. 0063000 

0. 012600 

Zinc. 

0. 0016052 

0. 000232 

Cadmium. 

A faint trace. 

A faint trace. 

Sulphur. 

None. 

0. 048934 


100 

100 

Ounces of silver to the ton. 

178.275 

231.408 

Ounces of gold to the ton. 

0. 026 

0.260 


The presence of tin in the bullion seems rather singular, inasmuch as it has not been detected in any of the 
ores or fluxes of Leadville. It has been suggested that it owed its origin to the great number of preserved-fruit cans 
scattered about the place, some of which may have found their way into the furnace. It is indeed said that these 
cans were at one time used at one smelter, probably as a precipitant for the lead in the galena. As tin has also 
been found in other products at different times, it seems hardly probable that this source can be adopted as that 
from which it is in all cases derived. 

The average assay of bullion shipped from Leadville during the early part of the census year was nearly 300 
ounces to the ton, but during the month of December, 1880, it had fallen off to less than 200 ounces. Mr. Guj*ard 
estimates the average loss of silver in smelting at 4.115 per cent., and of lead at 11.G8 per cent., part of which, 
however, is recovered from the chamber- and flue-dust. The bars of bullion weigh on an average 100 pounds each, 
200 bars, or 10 tons, constituting a car-load. They are shipped to eastern refineries, and when sold direct the latter 
pay the cost of transportation, which varies from $27 to $35 per ton. The price of lead in bullion is subject to great 
fluctuation, and has varied between $30 and $78 per ton at Leadville, the average price being $G0. Payments are 
made for bullion at New York quotations, deducting for the cost of refining 3 cents per ounce of silver, or sometimes 
$14 to $15 per ton of bullion. In other cases the charges are 3 ounces of silver and 5 per cent, of lead per ton. 

Slag. —The slags produced at Leadville are in some instances normal singulo-silicates, but in general rather 
more acid, the object in producing the latter being to insure a smoother run of the furnace, to require less constant 
watching and to ovoid the formation of sows and accretions. They flow freely, and generally possess, when cold, a 
compact, fine-grained structure, though frequently well crystallized in parts. They are for the most part strongly 
magnetic; and Mr. Guyard has shown that this property is not due to any magnetic silicate of iron, but to magnetic 
oxide of iron, he having isolated these substances in a greater or less quantity and in a state of perfect purity from 
all slags investigated by him. As a means of judging whether the slag is normal in its composition and contains 
any excess of lead determinations are made daily at a few of the smelters by means of the Jolly spring-balance. 
Slags from a normal run carry from 2 to 4 per cent, of lead and from 2 to 4 ounces of silver to the ton, though by 
attention and careful charging these figures are sometimes greatly lowered. On the other hand, they frequently 
run much higher, both in lead and in silver, owing to the faulty composition of the charges or to careless regulation 
of the smelting process. Slags from the earlier campaigns of some furnaces have been found to contain as much 
as 15 to 20 per cent, of lead, and silver in proportion; in view of which it is hardly a matter of wonder that failures 
were frequent. Slags accidentally rich in silver, and whole slag heaps from some of the works first started are 
re-smelted with the ores. 

Mattes. —Since the sulphide ores occurring in the region are not roasted, but thrown directly into the 
furnace, mixed iu small proportion with the oxidized ores, a certain amount of matte is necessarily formed, which 
consists mainly of sulphides of iron and lead, with, as ascertained by Mr. Guyard, a large percentage of magnetic 
oxide of iron. These mattes carry from 40 to 90 ounces of silver to the ton, and are roasted in heaps preparatory 
to being re smelted. 































294 


PRECIOUS METALS. 


Speiss. —Speiss, which is found only in small quantity, is an iron sulph-arsenide, and seems to concentrate in 
Itself all the molybdenum as well as most of the nickel, traces of which exist in the ores. It is further characterized 
by its very small percentage of antimony, and, according to Mr. Guyard, by the total absence of cobalt. It is a 
question, however, whether an examination of a large number of samples would justify the conclusion drawn by 
Mr. Guyard that a complete separation of nickel and cobalt is effected in the smelting process. He found cobalt 
without nickel in the skimmings from the lead-wells and nickel without cobalt in the speiss. 

Its silver contents vary from 2 to 4 ounces per ton. It is not roasted or subjected to any further treatment. 

Accidental formations in the furnace.— Among these iron sows are the most important, and have 
frequently been the source of much trouble, sometimes necessitating, as before mentioned, the blowing-out of a 
furnace in order to effect their removal. Besides ordinary hearth obstructions, different shaft accretions are found 
in varying quantity, which it is unnecessary here to discuss further, save to quote an instance, mentioned by Mr. 
Guyard, of a small, round furnace entirely lined from the water jackets to within G inches of the feed-hole with one 
of these accretions a foot in thickness. 

Flue- and chamber dust.— Leadville being situated at an elevation of 10,000 feet above the sea, the volume 
of air blown into a furnace with a given blast-pressure is far greater than with the same pressure at sea-level; 
consequently the draught of the furnace is correspondingly increased, and the quantity of dust and fumes escaping by 
the stack is very large. This would seem to necessitate the employment of a very perfect system of condensing flues 
and chambers. In point of fact, however, as has been seen, these arrangements are, with one or two exceptions, 
very poor; consequently a large proportion of the dust and fumes is lost in the air. Their composition is extremely 
complicated, and is characterized by the presence, in considerable quantities, of chlorides, bromides, iodides, and 
phosphates. They carry from 25 to 60 per cent, of lead, the latter figure applying to the fumes condensed in the 
Bartlett filter before described, and from 30 to 40 ounces of silver to the ton, although the Bartlett filter fumes 
held but 4.3 ounces. The composition of the latter is otherwise remarkable in that they contain over 11 per 
cent, of phosphate of lead, 9 per cent, of chloro-bromo-iodide of lead, and 18 per cent, of sulphide of lead, and 
from the further fact, according to Mr. Guyard, that iron, zinc, and manganese exist in them entirely in the state 
of sulphides. It must be borne in mind, however, that these fumes were condensed at a distance of 200 feet from 
the furnace. Mr. Guyard has calculated the weight of calcined dust collected from one furnace of 30 to 40 tons 
capacity during twenty-four hours at 1,400 pounds, and estimates that, where the filter is not employed, the loss of 
lead equals half a ton and of silver 4£ ounces per day per furnace. On this assumption more lead is lost in the air 
than is collected in the dust-chambers. As already shown, the chamber- and flue-dust is mixed with lime and thrown 
over the ore-beds to be re-smelted. In one case, however, a furnace was specially constructed for the purpose of 
roasting the flue-dust, though with what object in view it is impossible to say, unless on the erroneous supposition 
that much arsenic is present. In point of fact, arsenic is found in it in only small quantities, and this roasting 
deprives the dust of the carbon which would otherwise suffice for the reduction of all the lead contained in it, 
besides occasioning the loss of some silver. In another smelter the flue-dust is prepared for re-smelting by melting 
down iu a reverberatory furnace, at first with, and now without, the addition of slag. It is then run out, and 
after cooling it is broken up and mixed with the charges. 

COST OF LABOR AND MATERIAL. 

Below are given a few data relative to the prices paid for Huxps, fuel, and the average wages of employes 
during the census year at Leadville, which serve to give a fair idea of the economic conditions of smelting at that 


time: 

Dolomite, per ton. $3 00 to $4 00 

Hematite, per ton... 8 00 to 11 50 

Charcoal, per bushel. 10 to 18 

Coke, per ton. 25 00 to 00 00 

Pine wood, per cord of 2,000 to 3,0u0 pounds. 4 50 to 5 00 

Foremen, per shift of eight to twelve hours. 3 00 to 6 00 

Head smelters, per shift of eight to twelve hours. 3 00 to 4 25 

Slag wheelers, per shift of eight to twelve hours. 2 50 to 4 00 

Feeders, per shift of eight to twefve hours. 3 00 to 4 00 

Helpers, per shift of twelve hours. 2 50 to 3 00 

Day laborers, per shift of ten to twelve hours.-. 2 50 

Engineers, per shift of eight to twelve hours. 3 50 

Fuelmen, per shift of eight to twelve hours. 3 00 















LEAD SMELTING AT LEADVILLE, COLORADO. 


295 


Conclusion.— lu conclusion, it may be said that lead smelting, as carried on in this region, while not entirely 
beyond criticism, has been brought to a relatively high degree of perfection, and is extremely creditable to American 
metallurgists. One of the most useful practical lessons that has been taught by the comparative success of the 
various smelting works is that this has been proportional to the more thorough training in scientific metallurgy of 
its managers, the completeness and accuracy with which they have gauged the operations of fheir furnaces by 
chemical tests, and the intelligence with which the results of these tests have been applied to the practical conduct 
of their business. 

Could this lesson overcome the idea so common among us that the adaptability and “cuteness” of the American, 
which is in so many points acknowledged to be superior to that of other races, enable him to master the science 
of smelting as readily as he does any branch of trade, it might prevent an increase of the already very considerable 
number of abandoned smelters which dot our western hills and valleys, and save a portion of the capital which is 
annually wasted through gross ignorance in the various operations connected with mining. 


















1 i 

■ 











































. 










































